MILWAUKEE – If the Mets could just get into this postseason derby, almost everyone thought it was a win. And it was. But now that they’re here, they’re acting like they belong, and besides, they’re playing like they could stay for a while.

The Mets’ mood and their moves give them a chance to end things in October. Even if they get past the Brewers, they will once again be underdogs in the second round against the rival Phillies, a stacked team that some call the favorite to win it all. But the Mets are now showing they have a chance in a wide-open league. This is why…

1. The Mets are acting like they’ve been here before.

No one, except their own baseball president David Stearns, expected them to be in the playoffs. But now that they’re here, they seem bewildered, and that’s a plus. As they celebrated a lively champagne-and-cigar party after sneaking into proceedings in game No. 161 in Atlanta, the day after the regular season was set to end, there was no indication from their demeanor whether they had won or lost at all. after beating 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 why they are handling things so well. People on the team say he is as positive as anyone they have ever known. He believed, or at least acted as he did, even when it was 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 from him.

2. The Mets get big contributions from so-called complementary players.

Jose Iglesias, who hit .337 in the regular season (good enough for a batting title had he qualified), will likely finally end his four-year streak 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: “The analytics screwed him.”

He was a part-time player early on, but between continuing brilliant play both ways and Jeff McNeil suffering a broken wrist (recent evaluations suggest it’s healing well and he could be back if the Mets go all out and give him want to return), Iglesias became a key figure in the infield and the lineup. He has batted 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 perhaps their best bargain since picking up RA Dickey for a similar issue. But there were many. All of these other contributors started 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 with an MLB minimum of $740,000 is as big a bargain as Iglesias and looks like a pillar for the future after taking a few years to flesh out his plans. Vientos was on the trade block a few years ago, and while he was more highly regarded at the start of this season, Brett Baty’s second-year struggles were just as much of a catalyst for Vientos’ promotion. Vientos, who slugs better than Pete Alonso (and everyone else), looks like a core piece whether at third base or first base. (Of course, that could depend on whether they re-sign Alonso.)

The quartet of Butto, Stanek, Garrett and Maton helped remake nearly half of a previously troubling bullpen. Butto has looked good as a starter, but he is downright dynamic in relief. Stanek fires bullets at 90 miles per hour and provides a late-inning option if star closer Edwin Diaz is unavailable, 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 is not far behind. And besides, he came from the Crosstown Yankees, and for $100,000. Who knew the Yankees were so generous to help their neighbors? Torrens doesn’t hit like Francisco Alvarez, but he’s actually a better pitcher and can help stop the running game, which is important in a postseason that has featured mostly low-scoring games so far.

3. They are a real team.

Scouts love the team’s “selfless” play so far. They notice big changes in September, including hitting behind runners, taking pitches so teammates can steal and shortening by two strikes. The team concept is alive and well here.

4. Their superstar plays like a superstar.

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 per month), Lindor really 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 perhaps the most important home run in Mets history in that fateful first game in Atlanta, securing the game’s second comeback and capping a season-long comeback for the ages .

Lindor always acted like this Mets team was a threat, and he seems intent on proving that. If he can’t beat Ohtani, he’s still putting together one of the best individual seasons for an everyday player in Mets history. He is also a team man. He never talked about the MVP race, only we did.