MILWAUKEE — If the Mets could just get into this postseason derby, it would be a win for just about everyone. And that was it. But now that they’re here, they act like they belong, and more than that, they act like they might stay for a while.

The Mets’ mood and moves give them a chance to go some distance in October. Even if they get past the Brewers, they will once again be underdogs in the second round against the rival Phillies, a strong team that some call favorites to win. But the Mets are now showing that they have a chance in an open competition. Here’s why…

1. The Mets act like they’ve been here before.

No one except their own baseball president David Stearns expected them to make the playoffs. But now that they’re here, they seem at a loss, and that’s a plus. After sneaking into the action in Game No. 161 in Atlanta the day after the regular season was supposed to end, they celebrated wildly with champagne and cigars, but it was impossible to tell from their demeanor whether they had even won or lost after they had defeated the Brewers 8-4 in the first game of the wild card series. This is a positive sign.

Mets manager Carlos Mendoza is one of the main reasons 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 behaved that way, even when the score was 0:5 and 22:33.

“I always knew we had really good players and at some point we would turn things around,” Mendoza said. “We never panicked.”

That’s all him.

2. The Mets are getting big contributions from the supposed supplemental players.

Jose Iglesias, who hit .337 in the regular season (good enough for a batting title had he qualified), will presumably finally be able to end his four-year streak of earning a relief contract in the minors League had to accept. It’s difficult to understand. JD Martinez offered as good a theory as any for Iglesias’ undeserved unpopularity: “Analytics screwed him over.”

He was a part-time player to start with, but between continued brilliant play in both directions and Jeff McNeil’s broken wrist (recent research suggests it’s healing well and he could be back if the Mets go very far and want him back), Iglesias became a key man in the infield and lineup. He had scored in 23 consecutive games before Game 2. There seems to be more.

Iglesias is a godsend at $1.5 million (OMG is he ever!) and might be their best bargain since they hired RA Dickey for a similar song. But there were many. All of 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.

With an MLB minimum value of $740,000, Vientos is as much of a bargain as Iglesias and looks to be a mainstay going forward after taking a few years to get used to his plans. Vientos was on the trade floor a few years ago, and while he was held in higher regard earlier this season, Brett Baty’s second-year struggles were the main impetus for Vientos’ rise. Vientos, who can hit better than Pete Alonso (and everyone else), looks to be a centerpiece whether at third or first base. (Of course, that could depend on whether they re-sign Alonso.)

The quartet of Butto, Stanek, Garrett and Maton helped revamp nearly half of a previously worrisome bullpen. Butto seemed fine as a starter, but he’s downright dynamic in relief. Stanek fires 99 mph and provides a late-inning option when star closer Edwin Diaz is unavailable, as was the case in Game 1. Maton is a guy who doesn’t get nervous, exactly the guy you need in October.

If Iglesias is the bargain of the year, Torrens isn’t 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 shooter 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.

The scouts are enthusiastic about the team’s “selfless” play so far. They notice big changes in September, including hitting behind runners, winning throws to allow teammates to steal, and going short by two. The team spirit is lived here.

4. Your superstar plays like a superstar.

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

Even though he’s injured, he’s the Mets’ most important man. Exhausted and still bothered by back pain, 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 completing a comeback for the ages.

Lindor has always acted like this Mets team is a threat, and he seems intent on proving it. Even if he can’t outdo Ohtani, he’s still in the process of 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 MVP competition, only we talk about it.