A magnificent Alexandre Lacazette free kick sent Arsenal into the Europa League semifinals with a comfortable 1-0 win away to a toothless Napoli on Thursday, ending Serie A's interest in European competition this season.

The Frenchman struck in the 36th minute to earn Arsenal a tie against Valencia, just as Napoli, trailing 2-0 from the first leg, were threatening to take control of the game.

Carlo Ancelotti's team lost their way after that and, although the hosts had 67 percent of possession, Arsenal were able to sit out the second half to reach the semifinals for the second season in a row with a 3-0 aggregate win.

"We came here with ambition, we wanted to win, to score some goals. We did it, and kept a clean sheet as well, which is important for the confidence," said Arsenal defender Laurent Koscielny.

Ancelotti said that "the game lasted 30 minutes."

"We had two chances to score and we didn't succeed," he added. "We have not been as lucid in the last two months, we are more predictable and because of that, we have difficulty with our finishing."

In a lively opening half hour, Napoli threatened to make a breakthrough as Jose Callejon's effort was saved by Petr Cech's legs and Arkadiusz Milik had a goal chalked off for offside.

The Pole should have put Napoli ahead minutes later when compatriot Piotr Zielinski's cross found him unmarked in the penalty area but he headed wide.

Arsenal also lost Aaron Ramsey to an apparent hamstring problem but, just as it seemed things were going against them, they went ahead as Lacazette curled his free kick around a poorly organised wall from 25 metres.

Arsenal should have wrapped up the game four minutes into the second half but Pierre-Emerick Aubameyang, with only Alex Meret to beat, placed his shot too near the goalkeeper who was able to save.

The second half petered out after that as Arsenal sat back and Napoli enjoyed most of the possession but did little with it.

Lorenzo Insigne shot weakly at Cech after getting clear of the Arsenal defence and was immediately substituted, a decision which infuriated the forward who watched the rest of the match on the touchline with his arms folded.

Fabian Ruiz summed up their evening by firing their last chance wildly over the crossbar in stoppage time.

"Insigne was just disappointed with the way the match went, he had believed in our chances like everyone else," said Ancelotti. "His reaction was not linked to the substitution."

Chelsea reached the Europa League semifinals by beating Slavia Prague 4-3 in a roller-coaster game on Thursday, helped by a Pedro brace in a first-half onslaught before withstanding a comeback bid by the Czechs after the break.

Chelsea, who will face Eintracht Frankfurt in the last four, were cruising 4-1 at halftime but Slavia's Petr Sevcik slammed home two strikes early in the second half, narrowing the aggregate score to 5-3.

With the Stamford Bridge crowd increasingly unsettled, and Slavia being roared on by their travelling fans, Sevcik spurned a chance to cut the deficit further.

But Chelsea, having won the first leg 1-0, held on to set up a semi against Eintracht, who beat visiting Benfica 2-0 to go through on away goals after a 4-4 aggregate scoreline.

A Chelsea triumph in the Europa League, a trophy they won in 2013, would secure a way back into the prestigious Champions League if they finish outside Premier League top four this season. They currently sit fifth in the table.

There was little hint of the tension to come when Chelsea raced into a 3-0 lead within 17 minutes, starting with Pedro chipping goalkeeper Ondrej Kolar after exchanging passes with Cesar Azpilicueta and Olivier Giroud in the fifth.

The Spain winger hit the post four minutes later only for the ball to rebound off Simon Deli's face for an own goal.

It was Pedro who carved out Chelsea's third when he squared for a simple finish by Giroud and the scurrying Spaniard claimed Chelsea's fourth in the 27th minute when he converted a rebound after Kolar saved from Giroud.

A minute earlier, Slavia's captain Tomas Soucek had given the boisterous Czech fans something to cheer when he powered in a header from a corner, leaving the door open for the visitors' improbable attempt to turn the game around.

Chelsea coach Maurizio Sarri said he had to get to the bottom of the familiar problem of his side losing their way in the second half of matches.

On Sunday, Chelsea conceded two goals shortly after the break in a 2-0 defeat at Liverpool in the Premier League, a pattern seen in other games.

"As usual in the last two months we started very badly in the second half," Sarri told reporters. "It's a big problem... We need a solution, we need to solve this problem."

Sarri, who has never won a major final as a coach, said he was determined to see his side triumph this time.

"For me, I think it is very important first of all to get to the final, but this time I don't want to just get to the final, I want to win the final," he said.

Slavia coach Jindrich Trpisovsky lamented his side's defensive performance in the opening 45 minutes.

"If we had managed the first half better, I think we could have gone through," he said. "Everyone says the English Premier League is the example to follow and that we cannot play against teams like this. But I think we showed today that we can."

American soccer players are objecting to the decision by the U.S. Soccer Federation to have them play Venezuela at Cincinnati's Nippert Stadium, claiming the playing surface is dangerous.

The match will serve as the U.S. team's final preparation match ahead of the 2019 Gold Cup, and will also mark the first time the U.S. has played in Cincinnati.

The U.S. National Soccer Team Players Association (USNSTPA) released a statement opposing the match, which will be played on a temporary grass field on top of the venue's artificial turf.

"The United States Soccer Federation is not advancing the interests of the sport of soccer or the interests of the players or the fans, but is solely focused on generating ever-increasing revenues and profits for the federation, its employees, its sponsors, and private businesses associated with the federation," the union said in a statement Thursday.

The union released an April 2 email it said it sent to USSF President Carlos Cordeiro in which players said the friendly "would be waste of time and resources, is a threat to player safety, and would be damaging to the effort to develop the United States men's national team and help the team achieve competitive success."

Nippert Stadium is the home of Major League Soccer's expansion Cincinnati team. The USNSTPA said "a game played on sod on top of artificial turf will be a waste of 90 minutes and also presents a substantially increased risk of player injury."

Reports have also stated that the U.S. will play Jamaica at Audi Field in Washington, D.C. four days earlier, though no official announcement has been made.

Venezuela is coming off an impressive 3-1 victory over Argentina in Madrid last month. The U.S. will begin play in the Gold Cup nine days after the Venezuela friendly, starting with a match against Guyana on Tuesday, June 18 in Saint Paul, Minn.

Following that match, the U.S. moves east to face Trinidad & Tobago on Saturday, June 22 in Cleveland before closing group play against Panama on Wednesday, June 26 in Kansas City, Kan.

The final is scheduled for Chicago's Soldier Field on July 7.

Information from ESPN FC's Jeff Carlisle and The Associated Press was used in this report.

Pedro scored twice to help Chelsea into the Europa League semifinals as 5-3 aggregate victors over Slavia Prague after a 4-3 win at Stamford Bridge on Thursday. On a day when his former club Napoli were eliminated, the win and progression preserves Maurizio Sarri's one remaining hope of winning silverware in his first season in England.

Positives

Chelsea set about their opponents with the speed, fluidity and intensity that Sarri wants to see in every match, and they were rewarded with a comfortable half-time lead that left their semifinal place in little doubt. There were no fresh injuries -- despite an early scare for Eden Hazard -- and Pedro was much improved

Negatives

What does Sarri say to his players at half-time? This was another second half that Chelsea began in a complacent haze, allowing Slavia to transform what should have been a comfortable passage into the Europa League semifinals into a tense and tetchy finale.

Manager rating out of 10

6 -- Sarri's starting XI began this match with everything he wanted from them, and they did enough first-half damage to reasonably put the tie to bed. Chelsea's habit of collapsing immediately after half-time really doesn't reflect well on him, though, and is a trend he cannot afford in the coming weeks.

Player ratings (1-10; 10 = best. Players introduced after 70 minutes get no rating)

GK Kepa Arrizabalaga, 5 -- His tendency to punch high balls that would be easy to catch appears to unsettle those around him, and it certainly didn't ease the second-half anxiety at Stamford Bridge. He also was beaten too easily for Petr Sevcik's first goal, though he wasn't culpable for Slavia's other strikes.

DF Cesar Azpilicueta, 6 -- Chelsea's most solid defender on a far-from-solid evening, he can point to the fact that the majority of Slavia's most threatening moments happened on the other side of the pitch. Did his best to keep those around them from becoming too rattled -- with mixed success.

DF Andreas Christensen, 5 -- Handled the threat of Lukas Masopust reasonably well, but the movement of replacement Peter Olayinka caused him problems, along with Slavia's increasingly ambitious midfield runners. Sarri was visibly frustrated with his uncertainty at times.

DF David Luiz, 4 -- Had little to do as Chelsea dominated the first half, but when called upon to provide a steadying presence at the heart of the home defence in the absence of the injured Antonio Rudiger, he fell short of what was required. Also went close to conceding a penalty when he handled a high ball.

DF Emerson Palmieri, 5 -- Goalkeeper Ondrej Kudela had no idea what to do whenever he sprinted forward to overlap Hazard, and one such run enabled him to centre the ball for Pedro to score his second after Ondrej Kolar had parried Olivier Giroud's shot. Didn't get anywhere near close enough to Sevcik for either of his goals, though.

MF N'Golo Kante, 7 -- His surging runs and incisive passes carved the visitors open at will in the first half, with one clipped ball in from the right flank creating a promising opportunity that Ross Barkley couldn't maximise. There were fewer flashes of what he does best after the break, but this was still a good display.

MF Mateo Kovacic, 5 -- Distributed the ball well enough early on from the "Jorginho position" at the base of Sarri's midfield but shows few instincts when it comes to protecting his back four, contributing to Chelsea's startling vulnerability, as Slavia rallied behind Sevcik's shooting.

MF Ross Barkley, 6 -- Started brightly, shifting the ball sharply to Hazard in transition in the lead-up to Pedro's opener and looking to drive forward whenever he could. Could not steady Chelsea as they lost their way at the start of the second half, however, and was sacrificed for Jorginho on 70 minutes.

FW Pedro, 7 -- Has looked his age (31) in recent months but was considerably sparkier here, initiating slick one-twos with Cesar Azpilicueta and Giroud for Chelsea's opener and also netting their fourth. Also accidentally created Simon Deli's own goal with perhaps the worst finish of his career.

FW Olivier Giroud, 8 -- It's hard to see him getting his wish of being Chelsea's first-choice striker next season, but he did everything he could here to bolster his case. Aside from Europa League goal No. 10, there were all the slick lay-offs and smart hold-up play that make him so valuable to this team.

FW Eden Hazard, 7 -- Gave everyone at Stamford Bridge an early scare when he stayed down after being kicked twice in the first two minutes, but he picked himself up to involve himself in much of Chelsea's best attacking play. Was finally replaced by Willian on 65 minutes.

Substitutes

FW Willian, 7 -- Provided energy and defensive work rate in place of Hazard when Chelsea needed a bit more defensive stability, though none of his attacking contributions yielded anything significant.

MF Jorginho, N/R -- Once again harshly booed by sections of Stamford Bridge when he replaced Barkley, he put one or two passes astray but did OK.

FW Callum Hudson-Odoi, N/R -- His every touch was met with palpable anticipation, but this was not a memorable cameo.

Big Picture

Kolkata Knight Riders' over dependence on Andre Russell is no state secret. In fact, it's more by design than accident. However, it is around the allrounder Russell that their team was built. The problem here is Russell, the bowler. He has conceded over ten runs an over, without completing his quota of four overs even once this season.

Against Chennai Super Kings at home, Russell leaked 16 in a momentum-shifting third over. Wickets through the middle kept Knight Riders in the contest but the lack of a fast-bowling option against the likes of Suresh Raina and Ravindra Jadeja hurt them in the end.

Russell's fitness remains the other issue for Knight Riders; having hobbled around and off fields earlier in the tournament, he suffered another injury scare during practice in the lead-up to Friday's game against Royal Challengers Bangalore, but remains in contention to play. Regardless, perhaps it's time for Knight Riders to look at Russell purely as a batsman and pick another seamer, either at the expense of a batsman or a spinner, to give themselves a better chance of restricting oppositions. Kerala seamer Sandeep Warrier could come in, should that happen.

They are up against a side that knows a thing or two about losses piling up, but with playoff qualification only a distant theoretical possibility now, Royal Challengers unwittingly become the danger team you don't want to lose to. If the threat still seems too meek, the availability of the newly signed Dale Steyn should change that, after coach Ashish Nehra described the chances of the pacer playing as "very high".

In the news

Andre Russell has suffered another injury scare; he took a blow to the shoulder in practice two days before the match, and went for X-rays on match eve. While captain Dinesh Karthik confirmed that Russell remains in the team's plans for Royal Challengers, he said a final call would be taken closer to the match. West Indies, too, would be keeping their fingers crossed on this front, given they are due to name their World Cup squad on April 23.

Previous meeting

Andre Russell belted 48 off 13 balls as Knight Riders equalled their own record of chasing the most runs in the last three overs: 53. Astonishingly, they did this with five balls to spare.

Likely XIs

Kolkata Knight Riders: 1 Chris Lynn, 2 Sunil Narine, 3 Nithish Rana, 4 Robin Uthappa, 5 Dinesh Karthik (wk, capt), 6 Shubman Gill, 7 Andre Russell, 8 Piyush Chawla, 9 Kuldeep Yadav/Sandeep Warrier, 10 Prasidh Krishna, 11 Harry Gurney/Lockie Ferguson

Royal Challengers Bangalore: 1 Parthiv Patel (wk), 2 Virat Kohli (capt), 3 AB de Villiers, 4 Moeen Ali, 5 Marcus Stoinis/Shimron Hetmyer, 6 Akshdeep Nath/Shivam Dube, 7 Pawan Negi, 8 Yuzvendra Chahal, 9 Dale Steyn, 10 Navdeep Saini, 11 Kulwant Khejroliya

Strategy punt

• The spin trio of Sunil Narine, Piyush Chawla and Kuldeep Yadav have struggled against left-handers this season, conceding 230 runs in 28.2 overs, with only three wickets between them. Will that tempt Royal Challengers to team-up Moeen Ali, who has been in good form, and Shimron Hetmyer, who was left out after a few early failures, in the middle order? With Marcus Stoinis hardly bowling, it might be worth giving Hetmyer a few more opportunities, regardless.

• Moeen Ali averages nearly 38 at a strike rate of 171 at No.4 in the IPL. Those are his best numbers in any position in the league, giving RCB enough reason to stick with him in that position. From Knight Riders' point of view, Moeen has struggled most against the googly this season, dismissed thrice off the delivery that happens to be Piyush Chawla's stock ball.

• Moeen Ali bowls 82% overs his overs in the middle (overs 7 to 15), but averages just 17 at an economy rate of 6 runs per over against left-handers in the IPL. Will Virat Kohli gamble and throw the ball to Moeen if Sunil Narine opens the batting for Knight Riders?

Stats that matter

• RCB find three of their bowlers in the top 10 on the list of most expensive bowlers at the death (overs 17-20) in the IPL since 2015 (qualification: minimum 25 overs bowled at the death). Umesh Yadav leads the way, conceding 12 runs per over, Tim Southee finds himself placed third at 11.6 runs per over, and Mohammed Siraj occupies the seventh spot at 10.7 runs per over

• KKR spinners have the second-worst bowling average this season (41.2)

• KKR spinners are the second-most expensive this season (7.9 runs per over)

• RCB have lost all five matches when they have lost the toss. KKR have lost four of five matches when they have lost the toss