ST. LOUIS, Mo. — Somewhat lost in the build-up to a rarity — a one-off, makeup game crammed into an already packed road trip for the Mets — was the importance of the novelty. 

Carlos Mendoza’s group entered play 1 ½ games back in the fight for the last National League wild card, a battle in which the Cardinals are also trying to hang around.

With one big inning and, more notably, one more big start from Sean Manaea, the Mets put a dent in one challenger’s hopes. 

Behind Manaea, the Mets bounced back from a series loss in Anaheim with what technically is a one-game sweep, a 6-0 victory at Busch Stadium on Monday in which the Mets could have looked tired and instead looked inspired. 

For Game Four of a 10-games-in-10-days trip that spans over 8,000 miles, the Mets left California, spent the day in Missouri and were set to jet back west to Colorado. 

“I think we all are in consensus that we wouldn’t want it any other way,” said Harrison Bader, whose RBI double in the fifth inning provided insurance. “It’s like a thing in baseball, we always say: Nobody cares. The game doesn’t care. The game doesn’t have feelings about what you’re going through, whatever is happening off the field, your travel schedule, the heat, all these things. If no one cares, why should we? 

“So we put our head down, we prepare the exact same way. We accept the challenge with grace.” 

There could have been bickering on a sweltering, Midwestern afternoon — a game played partly in the shadows that make hitting that much harder — but there isn’t much complaining these days from the Mets dugout when Manaea is on the mound. 

The lefty threw seven more shutout innings for the Mets (59-53), upping his streak to 14 in his past two starts, and was at his best when he needed to be. 

Manaea was not perfect on a day he allowed six hits, but he was perfect when the Cardinals (57-56) threatened.

St. Louis batters went 0-for-7 with runners in scoring position against Manaea, who typically saved his 10 strikeouts for when they would come in handy.

In back-to-back outings, Manaea has punched out double-digit batters, the first Mets lefty to do so since Sid Fernandez had a three-game streak in 1992. 

“I think he found a rhythm here where every pitch is working for him,” Mendoza said. 

Manaea danced into and out of trouble. 

In the third inning, the Cardinals put two on with two outs for Willson Contreras, who got ahead 3-1 in the count.

Manaea responded with an outside-corner slider and a 95.7-mph fastball that Contreras swung through, Manaea pounding his glove as he walked off the mound as a tone was set. 

In the fourth, the Cardinals put two more on base for Pedro Pages, who went to a knee whiffing on a good sweeper. In the fifth, it was Masyn Winn who reached second base with two outs before Contreras sent a drive to deep right, where Tyrone Taylor made a nice leaping catch against the wall for another Houdini act. 

“I wouldn’t say ‘different gear,’ ” Manaea said, explaining how he raised his game at big moments. “Just confidence in my fastball and slider.” 

At a time when there are plenty of questions surrounding the Mets rotation — Kodai Senga likely will be out for at least the regular season, Luis Severino’s velocity was down in his most recent outing and Jose Quintana was not crisp Sunday — Manaea has stepped up into a front-of-the-rotation type of pitcher. 

Ryne Stanek and Edwin Diaz finished off the Mets’ fourth shutout this season and received more help from the offense than they needed. 

The Mets scored first accidentally — Pete Alonso scoring from third on a wild pitch in the second inning — before the runs came more purposely.

An eight-batter, four-run fifth inning, keyed by a Taylor bases-clearing double, broke the game open, before Jeff McNeil’s solo shot added breathing room in the sixth. 

The Mets might not feel great physically, but they could board their plane in good spirits. 

“Our job is to continue to win baseball games,” Mendoza said, “regardless of the circumstances.”