ATLANTA -- Dansby Swanson and Matt Olson homered for the third straight game, Travis d'Arnaud hit a go-ahead two-run single in the third inning and the Atlanta Braves beat the New York Mets 5-3 on Sunday night to win a critical tiebreaker in their season series.

The defending World Series champion Braves swept the three-game series and moved two games ahead of New York in the National League East. Any combination of one Atlanta win or one Mets loss would give the Braves their fifth straight division title.

"It's a clubhouse full of guys who want to win," Olson said. "That's all it's been since the moment I walked in. That's No. 1 on the program."

New York plays its final games of the season against the visiting Washington Nationals, who are last in the division. Atlanta goes to the Miami Marlins. Both series start Monday.

Should the season end Wednesday in a tie, Atlanta would win the NL East because it won the season series 10-9.

"We've felt this confidence since the beginning of the year," d'Arnaud said. "It just didn't go our way early in the year, but pulling on the same rope, having each other's backs, not trying to do too much. We're just trying to play the game of baseball and have fun with it."

The Braves won five of the last six games in the series, outscoring the Mets 42-19 over that stretch. New York had a 10½-game lead on June 1, but it is now lower in the standings than at any point this season.

It was a lost weekend for New York, which came to Atlanta hoping to clinch its first division title since 2015. Instead, aces Jacob deGrom and Max Scherzer lost Friday and Saturday, respectively, before 15-game winner Chris Bassitt lasted just 2⅔ innings on Sunday.

Those three combined for a 2.79 ERA over 377 innings entering the series; they posted a collective 6.91 ERA over 14⅓ innings with six home runs allowed over the weekend.

"We still have three games left in the regular season, we're still going to the postseason, that doesn't change; but there's a lot of learning points that we can take from this series moving forward," Mets slugger Pete Alonso said. "I thought we played well, but the Braves played better. They played excellent baseball this entire weekend."

Baseball's new postseason format means the winner of the NL East will get a first-round bye into the divisional round as the second seed. The NL East runner-up will get the fourth seed and play in a three-game wild-card series, with the winner of that series moving to the divisional round.

Atlanta now stands on the doorstep of a fifth straight division title while also looking to repeat as World Series champion.

All three games here were sellouts, and the atmosphere all weekend was notable to Braves manager Brian Snitker.

"I said Friday ... to my wife, 'Well, the playoffs are starting today,'" he said. "This whole weekend felt like a playoff weekend. ... This is about as electric as I've seen [Truist Park] ... with NFL and college football, this place was still packed."

Swanson took Bassitt deep to right-center in the first with his 25th homer, and Atlanta took charge with a three-run third. Bassitt (15-9) issued a bases-loaded walk to Olson before d'Arnaud delivered a single up the middle to score Ronald Acuna Jr. and Austin Riley for a 4-3 lead. That chased Bassitt, who was charged with four runs, three hits and three walks.

Olson connected for his 33rd homer to make it 5-3 leading off the sixth, his 410-foot shot landing in the seats in right-center. Olson, in his first year with Atlanta, surpassed 100 RBIs for the second straight season.

"Everyone knew we were underperforming when we were flirting around that .500 range," Olson said. "It was one of those things where it was trusting the talent we have and the guys in the clubhouse. Everybody was solid, head down, do your work, it'll turn around and you wind up winning."

Charlie Morton stranded runners on first and second in the first, but he gave up Daniel Vogelbach's 18th homer that tied it at 1 in the second. The righty struck out Francisco Lindor with runners on first and second to end the threat.

Jeff McNeil went deep off Morton in the third, and Vogelbach followed with an RBI single to put the Mets up 3-1. Morton entered the game having allowed 28 homers, sixth most in the NL.

Morton scuffled throughout his start, giving up three runs and nine hits in 4⅓ innings as the 38-year-old made his first start since signing a $20 million, one-year contract to remain with Atlanta next season.

Dylan Lee (5-1) relieved Morton and pitched 1⅓ innings, leaving after a walk to Brandon Nimmo with two outs in the sixth. Collin McHugh entered and struck out Lindor.

Raisel Iglesias faced four batters in the seventh, A.J. Minter faced the minimum in the eighth and closer Kenley Jansen converted his third save of the series with a clean ninth.

Jansen leads the NL with 40 saves in 47 chances.

The Braves' bullpen, which posted a 1.70 ERA last month, pitched 8⅔ scoreless innings the past two nights.

"I am proud of everything they have done," Mets manager Buck Showalter said. "This is not conditional. It's unconditional, the support, and if I know these guys they will rebound and make somebody feel their pain."

ESPN's Kiley McDaniel and The Associated Press contributed to this report.