PORTSMOUTH, England -- Having experienced the white heat of a Flamengo-Fluminense derby and the frenzied expectation of the Copa Libertadores knockout rounds, Pablo Mari would not have been unduly worried by the prospect of a trip to Fratton Park, but he could have picked a less intimidating venue for his Arsenal debut all the same.

If Arsenal's progress to the FA Cup quarterfinals, courtesy of a 2-0 win, was comfortable enough in the end, the early stages were anything but. Portsmouth's players showed a readiness to get physical from the off, with Arsenal's young forward line coming in for some particularly rough treatment, and there were only 17 minutes on the clock when Lucas Torreira had to be carried from the field on a stretcher after his ankle buckled when he was caught by a robust challenge from Pompey centre-back James Bolton. The Uruguay midfielder left the stadium with his ankle in a brace and will now be assessed by the club's doctors.

There were fleeting echoes of the kind of roughhouse tactics that Arsenal would routinely face on away trips during the more fragile periods of the Arsene Wenger era. As Torreira lay on the pitch in agony receiving treatment from Arsenal's medical staff, a sizeable proportion of the home crowd cruelly chorused: "You're going home in a f---ing ambulance!" Even Tony Pulis, former manager of Arsenal's long-term betes noires Stoke City, was in attendance, albeit as a pundit on BBC radio rather than a glowering presence in the opposition dugout.

Mari, who has signed on loan from Flamengo until the end of the season, is likely to face sterner tests than that presented by League One promotion-chasers Portsmouth, whose manager, Kenny Jackett, made six changes to his starting XI, but the tall Spanish centre-back played an active role in helping Arsenal to withstand the hosts' early aggression.

Playing to the left of David Luiz, he consummately shut down livewire Portsmouth striker Ellis Harrison and won an important share of headers, most notably when bravely clearing a dangerous cross from Marcus Harness after the winger had smuggled his way past Sokratis Papastathopoulos on Arsenal's right flank in the early stages. But it was with the ball at his feet that Mari really caught the eye. Befitting a player who spent three years on the books at Manchester City, where he is likely to have come to the attention of his new manager Mikel Arteta, he looked smooth in possession and regularly sought to break the lines with penetrating passes into the feet of the visitors' attacking players.

"I think he looked comfortable," Arteta said. "He's very vocal, he's very comfortable on the ball and he's always commanding the back four. He looked like he'd played here for months."

Mari is the first left-footed centre-back to have signed for Arsenal since Thomas Vermaelen arrived from Ajax in 2009, and he therefore gives the team passing angles from the back that they have not possessed for some time. In a mirror image of Luiz, the 26-year-old regularly hit long, high diagonal passes out to the right flank, with one such delivery presenting Reiss Nelson with an opportunity to wriggle to the byline on the right and put in a cross that Gabriel Martinelli headed over the bar.

Nelson had made a quiet start to the game prior to that moment, but the 20-year-old came to life late in the first half and ended up delivering the crosses from which Sokratis and Eddie Nketiah scored the goals, either side of half-time, that put Arsenal in the hat for the last eight.

Nketiah has scored three goals in six games since being recalled from his loan spell at Leeds United, and increasingly has the look of a viable alternative to Alexandre Lacazette, whose past three Arsenal goals were spread across a period of more than two months. Nelson, meanwhile, showed the kind of incisiveness against Portsmouth that is often glaringly absent from the game of record signing Nicolas Pepe.

Arsenal should not really need alternatives in attacking positions, given the firepower at Arteta's disposal, but as last Thursday's calamitous Europa League exit against Olympiakos demonstrated, for all their ability, Lacazette, Pepe, Mesut Ozil and even Pierre-Emerick Aubameyang cannot always be relied upon to finish the job. Arteta left all four out of his starting XI at Fratton Park, with Joe Willock joining Nketiah, Nelson and Martinelli in a very fresh-faced front four, and the manner in which they refused to be cowed by Portsmouth's physicality put a smile on the manager's face.

"The kids responded really well," he said. "It's risky to play them in these competitions, but it's worth that risk."

Arsenal's Europa League elimination was the first black mark of Arteta's reign, cutting off as it did the club's most likely pathway to Champions League qualification, but he retains credit in the bank. Liverpool's surprise defeat at Watford on Saturday, which prevented Jurgen Klopp's side from emulating Wenger's 2003-04 Invincibles, unexpectedly gave Arsenal's fans something to smile about and there were joyful chants of "49, 49, undefeated!" from the away end as the clock ticked down against Portsmouth.

Arsenal will not want to keep harking back to that achievement forever, and the scars of Olympiakos are likely to take some time to heal, but in Mari's assured debut and the effervescence of Arteta's young players, there were hints of better days ahead.