MILWAUKEE — If the Mets could just get into this postseason derby, most everyone figured that was a win. And it was. But now that they are here, they are acting like they belong, and what’s more, playing like they may stay around a while.

The Mets’ mood and their moves give them a chance to go a distance in October. Even if they get past the Brewers, they will be underdogs again in round two against the rival Phillies, a stacked team some are calling the favorite to win it all. But the Mets are showing now that they have a chance in a wide-open competition. Here’s why …

Nobody, except their own baseball president David Stearns, expected them to be a playoff participant. But now that they are here, they seem nonplussed, and that’s a plus. While they had a spirited champagne-and-cigar celebration after sneaking into the proceedings in game No. 161 at Atlanta, the day after the regular season was supposed to end, there was no way to tell from their demeanor if they even won or lost after they beat the Brewers, 8-4, in Game 1 of the wild-card series here. That’s a positive sign.

Mets manager Carlos Mendoza is a big reason they are handling things so well. Folks around the team say he’s as positive as anyone they’ve ever known. He believed, or at least acted like he did, even when they were 0-5 and 22-33.

“I always knew we had really good players and at some point we were going to turn it around,” Mendoza said. “We never panicked.”

That’s all him.

Jose Iglesias, who hit .337 in the regular season (good enough for a batting title had he qualified), presumably will finally be able to end his four-year run of having to accept a make-good, minor league deal. It’s hard to understand. J.D. Martinez offered as good a theory as any for Iglesias’ undeserved unpopularity: “Analytics [screwed] him.”

He was a part-time player at the start, but between continuing brilliant play both ways and Jeff McNeil suffering a fractured wrist (recent evaluations suggest it’s healing properly and that he could be back if the Mets go very far and want him back), Iglesias became a key man in the infield and the lineup. He’d hit in 23 straight games heading into Game 2. It seems like more.

Iglesias at $1.5 million is a godsend (OMG is he ever!) and might be their best bargain since they picked up R.A. Dickey for a similar song. But there were many. All these other contributors began the season elsewhere or in the Mets minors: Mark Vientos, Jose Butto, Ryne Stanek, Reed Garrett, Phil Maton, Luis Torrens, Jesse Winker and Martinez.

Vientos at the $740,000 MLB minimum is just as big a bargain as Iglesias and looks like a mainstay going forward after taking a few years to work his way into plans. Vientos was on the trading block a couple years back, and while he was held in higher esteem to start this season, Brett Baty’s second-year struggles were as much the impetus for Vientos’ promotion as anything. Vientos, who’s slugging better than Pete Alonso (and everyone else), looks like a core piece, whether it be at third base or first. (That of course might depend upon whether they re-sign Alonso.)

The quartet of Butto, Stanek, Garrett and Maton helped remake almost half a previously worrisome bullpen. Butto looked OK as a starter but he’s downright dynamic in relief. Stanek is firing 99 mph bullets and provides a late-inning option when star closer Edwin Diaz isn’t available, as was the case for Game 1. Maton is a guy who doesn’t get flustered, just the kind you need in October.

If Iglesias is the bargain of the year, Torrens isn’t far behind. And what’s more, he came from the crosstown Yankees, and for $100,000. Who knew the Yankees were that generous to help out their neighbors? Torrens doesn’t hit like Francisco Alvarez, but he’s actually a better thrower and can help stop the running game, which is important in a postseason that’s featuring mostly low-scoring games so far.

Scouts are loving the team’s “selfless” play so far. They are noticing great changes in September, including hitting behind runners, taking pitches to allow teammates to steal and shortening up with two strikes. The team concept is alive and well here.

I don’t want to hear that Francisco Lindor as an MVP candidate was an example of East Coast bias. Before he hurt his back, and before Shohei Ohtani single-handedly took over September (1.225 OPS for the month), Lindor truly looked like he had an outside shot.

Even hurt, he’s the Mets main man. Exhausted and with back pain still shooting through him, he delivered maybe the most important home run in Mets history in that fateful first game in Atlanta, securing the second comeback of the game and finishing a comeback of ages for the season.

Lindor always acted like this Mets team was a threat, and he seems intent to prove it. If he can’t outdo Ohtani, he’s still putting together one of the best individual seasons for an everyday player in Mets history. He’s a team guy, too. He never talked MVP race, only we do.