MILWAUKEE -- Late Sunday morning, there were no obvious signs of anxiety within the Mets’ clubhouse. House music pulsed loudly from a large speaker at one end of the clubhouse. Players milled about, a few of them wandering onto the field to soak up a brilliant Wisconsin morning. For the uninformed, the stakes of the day were not obvious.

During those hours, the Mets spoke to each other about keeping their processes the same.

“I’ve been saying this since we sucked and everybody kind of wrote us off,” designated hitter J.D. Martinez said. “It’s like, ‘Dude, we don’t have any pressure. We’re not supposed to be here. We can’t get here now and all of a sudden put pressure on ourselves.”

So the Mets did not. Rather than cave under the weight of anxiety, they shook off three consecutive losses to produce one of their cleanest games of the season: a 5-0 win over the Brewers that ensured them a clear path to the postseason. Win one of their two games in Atlanta on Monday, and the Mets will make the playoffs.

“I’d sign up for that any day,” manager Carlos Mendoza said.

They have evidence to believe they can succeed. In a must-win game Sunday at American Family Field, David Peterson submitted one of the finest starts of his career, allowing one hit over seven innings with eight strikeouts. After a one-out walk in the second inning, Peterson retired 16 of the final 17 batters he faced.

“The way he controlled the game, his tempo, I don’t think there was any type of pressure,” Mendoza said. “He was calm, he was under control, and he kept making pitches.”

Along the way, the bats made sure that Brewers starter Colin Rea and two relievers were never comfortable. Francisco Alvarez returned from injury to drive in two runs. Jose Iglesias extended his hitting streak to 20 games. Perhaps most importantly, Francisco Lindor shook aside his back aches to go 2-for-4 with a homer, two RBIs, two runs scored and two stolen bases, proving that he can play at a star-caliber level despite not feeling his best.

“I’m in a good spot,” Lindor said. “The trainers are doing an outstanding job of keeping me in a good spot.”

The Mets, as a team, are all in a good spot, even though they can be eliminated from playoff contention on Monday. The way they see it, after starting 0-5 this season and sitting 11 games under .500 as late as May 29, they have nothing to lose.

But they do have everything to gain, with multiple scenarios still on the table.

• Dramatic doubleheader to decide final 2 NL Wild Card spots -- here's how

If the Mets sweep Monday’s doubleheader, they will earn the National League’s No. 5 seed and travel to San Diego for a Wild Card Series beginning Tuesday.

If the Mets take one of two from the Braves, they will earn the No. 6 seed and return to Milwaukee for a Wild Card Series beginning on the same day.

If the Mets lose both games to the Braves, their season will end without a playoff berth.

It is a layout that favors the Mets, because even if they lose Game 1 of the doubleheader, the Braves will have nothing left to play for and will hold their ace, Chris Sale, for the Wild Card Series. The Mets will employ a similar strategy, according to a source, pitching Tylor Megill in Game 1 and using Luis Severino for Game 2 only if necessary.

No matter who pitches over the course of 18 innings, the goal will be the same: win once. That’s all that matters.

“We’ve been playing important games for a long time now, and so we understand the magnitude of what these games hold for us,” Peterson said. “Nothing really changes. You prepare the same way. We’ve done all the work up to this point. We’ve played almost 162 games. For us, it was about coming out with a bunch of energy and competing and giving it everything we had.”

“This team just plays better that way,” added Martinez. “When we’re just having fun, messing with everybody in here, listening to [Iglesias’] ‘OMG’ song and making fun of him and stuff like that, just having a good time, it takes the pressure off everything. Especially with these games coming up -- it’s going to be the biggest thing for us.”