The Mets’ Pete Alonso, Francisco Lindor and teammates leave the...

The Mets’ Pete Alonso, Francisco Lindor and teammates leave the dugout after the 3-2 loss to the Washington Nationals in an MLB game at Citi Field on Sunday. Credit: Kathleen Malone-Van Dyke

The Mets walked off Citi Field to boos Sunday, likely never to return this year. Their 3-2 loss to the Nationals  was not only a depressing curtain drop to Fan Appreciation Weekend but set in motion a confluence of events that could keep them out of the postseason.

That’s because roughly 40 minutes later, shortly after 5 p.m., the score became final at Cincinnati’s Great American Ball Park, where the Reds again knocked off the Cubs, 1-0.

It was right at that moment, with the Mets packing for what could be their two-city road trip to oblivion, that Brandon Nimmo was told by a reporter that they no longer were in control of their playoff destiny. The Mets and Cincinnati have the same record (80-76) and the Reds hold the head-to-head tiebreaker.

Could Nimmo believe the Mets were in this precarious spot?

“Yes, I can believe it, because I’ve watched it,” he said. “I’ve been watching it happen right in front of us. I’ve been part of it and it’s not ideal. But we can still get into this thing. We still got to focus on winning ballgames. Nothing has changed.”

That’s not entirely true. Everything has changed for the Mets, who held baseball’s best record (45-24) on June 12, along with a 51/2-game lead atop the NL East, but have played to a .402 winning percentage (35-52) the rest of the way, tied with the White Sox for the fourth-worst in the majors.

The Mets also began September with a four-game lead over the Reds for the third and final wild-card spot. For comparison’s sake, the 2007 Mets — infamous for their own epic failure — began that season’s final month with only a three-game edge over the Phillies (which of course ballooned to seven before they kicked it away in the last 17 games).

 

What’s happening now isn’t a collapse in that ’07 sense, however. This has been more like a gradual but steady erosion — in performance, in ability, in spirit.

Teams go into tailspins occasionally. That’s baseball. But for a $340 million roster to be this bafflingly inadequate for so long, and now badly misfiring with the season on the line, that just defies explanation.

Take this weekend’s series loss to the lowly Nationals, one of those three teams with a more putrid winning percentage (.386) since mid-June. These essentially were playoff games for the Mets, who responded with terrible defense, mindless baserunning, disappearing bats and questionable managerial decisions by Carlos Mendoza.

Just when you thought it couldn’t get any more frustrating than Saturday’s extra-inning loss,  when Edwin Diaz was pulled after one seven-pitch inning and the Nationals rode an inside-the-park homer from Daylen Lile to victory, the Mets served up a second helping of humiliation in Sunday’s series finale.

This time Mendoza’s piggyback strategy backfired when starter Sean Manaea gave up three runs in only three innings-plus — the big blow coming on .185-hitting Nasim Nunez’s two-run homer in the second — and the Mets got burned by two circus catches by Jacob Young.

The centerfielder robbed Brett Baty of extra bases leading off the fifth when he juggled his long fly ball, then kicked it up in the air, hacky-sack style, before surprising himself with the grab.

In the ninth, the sprinting Young leaped to snag Francisco Alvarez’s 111-mph, 411-foot drive, taking away what would have been a tying homer to open the inning.

Young’s acrobatics not only spelled Sunday doom for the Mets but felt like bad omens for a team trying to stay alive down the stretch. If Mendoza & Co. couldn’t buck these disturbing trends going on 3 1/2 months now and come up with their best baseball against the 28-games-under-.500 Nationals, why should anyone think they’ll be able to do it for six more on the road against the Cubs and Marlins?

“We put ourselves in this position, so we got to find a way to get out of it,” said Francisco Lindor, whose throwing error Sunday led to the Nationals’ first run. “And that comes down to winning. We just got to win ballgames.”

While this year’s Mets have become a disappointing investment on the field for Steve Cohen, at least the fans responded to    the owner’s preseason challenge    by setting a Citi Field single-season attendance record as 3,182,057 showed up to see MLB’s second-highest payroll underachieve on a nightly basis.

There was a smattering of boos among Sunday’s sellout crowd, but Pete Alonso did get a standing ovation when he was replaced for a pinch runner in the eighth inning.

Alonso certainly will decline his $24 million player option for next season, so there is a chance that Sunday was his last game in Flushing in a Mets uniform.

We’d say the chances still are good that Cohen will bring him back again, but don’t count on the Mets returning to Citi Field in October, as they did with last year’s inspiring rebound. The same spark just hasn’t been there despite the Mets’ repeated claims that it really does exist.

“Winning solves everything at this point,” Alonso said. “We just gotta do it. Gotta solve our issues between the lines. That’s a simple fact.”

Here’s another one: The Mets now need help to leapfrog the Reds and make the playoffs. It’s become shockingly clear for a while that they can’t do it on their own.

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