With the Mets’ ace on the mound, with the Phillies’ ace set to take the mound on Sunday, with a three-game showdown against the skulking Braves looming, and with a sold-out, enthusiastic crowd on site, Saturday’s Mets game technically took place on Sept. 21, but had all the significance and flavor of October.

However, it wasn’t just the atmosphere that seemed worthy of the postseason: The Mets are playing like a playoff team.

On perhaps the loudest afternoon of the season in Queens, Sean Manaea was dominant and his offense was loud enough: A three-run seventh inning made the difference in the 6-3 victory over the Phillies in front of 44,152 spectators at Citi Field.

The Mets (86-69) waited for the Braves’ game in Miami to end and will finish that series against Zack Wheeler before their season could be decided in Atlanta starting Tuesday.

Carlos Mendoza’s team is facing its most significant showdown of the season after a worst-case scenario splitting a series against the Phillies, the leaders in the east of the NL.

Luisangel Acuña hit his third home run in just his eighth major league game and Francisco Alvarez hit his fifth home run in his last nine games.

However, the tied game was decided in the seventh inning when the Mets team, which had left too many players on base, finally took advantage of their opportunities.

Against dominant right-hander Orion Kerkering, the Mets became dangerous when they walked Starling Marte and drilled Pete Alonso (who had one hit but reached base five times).

With one out, Brandon Nimmo hit a single into left field and shouted to his dugout in joy and suddenly with a lead.

That lead was extended, and two batters later, Alvarez scored for a second time that day with a double that separated the outfielders and into left-center field for two runs.

The Phillies scored once in the eighth inning against Reed Garrett before Edwin Diaz came in with a runner on first base and Kyle Schwarber at bat.

Diaz made the possible tying point and – after a bloop from Alonso and an RBI single in the second half of the eighth inning provided additional security – Diaz eliminated the Phillies in the ninth inning.

The Mets and Phillies traded leads through the first five innings.

Schwarber’s home run on the second pitch of the game put the Mets in trouble.

Home runs by Alvarez and Acuna in the second inning gave the Mets the lead before Nick Castellanos reached out with his bat in the fifth inning and hit a solo hit over the left outfield boundary to tie the game at 2-2, setting the stage for the decisive seventh inning.

Even without Francisco Lindor, the Mets always seem to find a way to get out of these close games. And more importantly, they’ve found an ace.

Manaea once again put in an outstanding performance in seven innings, scoring three runs on three hits (two of them home runs), no walks and six strikeouts.

In 11 games since July 30, the left-hander has allowed four runs just once and has an ERA of 2.50.

He was efficient, needing only 89 pitches to get to the eighth inning.

After Manaea allowed a leadoff single to JT Realmuto, the fifth-largest crowd in Citi Field history gave him a standing ovation, and Manaea returned the gesture with a tipped cap and an air kiss.

The Mets’ pitching and late-game offense kept them from regretting earlier missed opportunities, including a rebound that went in the Phillies’ favor in the sixth inning.

With Harrison Bader on first base and two out, Acuña sent a bloop down the right field line that was just within reach of the sliding Castellanos.

Castellanos was out of the game and center fielder Johan Rojas was far away. The ball bounced off the ground and landed in the seats, resulting in a grounds rule double that kept Acuña on second base and Bader on third, tying the game.

Had the ball stayed on the field, he would have scored at least one run and the speedy Acuña might have been able to hit an inside-the-park home run.

Instead, Jose Iglesias stepped forward and threw the ball back to Jose Ruiz, who knocked the ball down, recovered and threw it out to escape.

Manaea, Diaz and some important swings made sure the rebound was forgotten.