Mets relief pitcher Edwin Diaz walks off the field after...

Mets relief pitcher Edwin Diaz walks off the field after Washington Nationals' Kurt Suzuki hit a game-winning three-run home run in the ninth inning of a baseball game Tuesday, Sept. 3, 2019, in Washington. Washington won 11-10. Credit: AP/Patrick Semansky

WASHINGTON —  The Mets found a stunning new low Tuesday night.

Up by six with three outs to go, the Mets lost to the Nationals, 11-10, after three pitchers combined to allow seven runs in the bottom of the ninth.

Edwin Diaz took the loss and the blown save, allowing a walk-off, three-run home run to Kurt Suzuki after a two-run double by Ryan Zimmerman. He inherited a bases-loaded, one-out mess created by Paul Sewald and Luis Avilan and did not record an out, needing only 10 pitches to complete the meltdown.

Thr  loss marked the largest lead blown by the Mets in the ninth inning or later in franchise history.

The Mets, 70-68 and five games back of a National League wild card spot with 24 games to play, were despondent in the visitor’s clubhouse at Nationals Park.

“This might be the toughest one of the season,” said Jeff McNeil, who was 2-for-5 with a homer and three RBIs in what was almost a blowout win. “We had it.”

Said Brandon Nimmo, who also homered: “When I came in here, I didn’t really know what just happened. It kind of just seemed like a bad dream. I don’t know. That’s hard to do even in a Little League game I feel like, come back from (six) runs down in the bottom of the ninth against guys throwing 99 miles an hour. I don’t really have words for that.”

Washington Nationals' Kurt Suzuki celebrates as he rounds the bases...

Washington Nationals' Kurt Suzuki celebrates as he rounds the bases after hitting a game-winning three-run home run in the team's baseball game against the New York Mets, Tuesday, Sept. 3, 2019, in Washington. Washington won 11-10. Credit: AP/Patrick Semansky

The Mets opened it up with five runs in the top of the ninth, aided by Matt Adams’ missed catch on a foul pop-up and Trea Turner’s mental lapse when he fielded a grounder and threw to first base instead of going for an inning-ending double play. McNeil capitalized with a two-run single, and Pete Alonso hit his 44th homer of the year, tied for most in the majors.

With the game seemingly in hand, manager Mickey Callaway pulled Seth Lugo, who had tossed 10 pitches in a scoreless eighth, in favor of Sewald. Callaway could have stuck with Lugo, his most effective and reliable reliever, but he chose to remove him in the hopes of having him Wednesday.

“When you have a six-run lead, major-league pitchers got to be able to hold that,” Callaway said.

And then an incredible series of events unfolded. The Mets led, 10-4, as Sewald entered. They had a win expectancy of 99.7 percent, according to FanGraphs. Teams leading by at least six runs with three outs to go were 274-0 this year, according to ESPN.

Victor Robles singled and Howie Kendrick flew out. Then Turner doubled, 10-5. Asdrubal Cabrera, the former Mets infielder, singled. Anthony Rendon singled, 10-6.

“I felt really good. I felt ready,” Sewald said. “I made some good pitches that they got hits on. I made a couple bad pitches and they got hits on this, too.”

Avilan replaced Sewald for one batter, Juan Soto, who singled to load the bases.

In came Diaz. Zimmerman, a close friend and former client of Mets general manager Brodie Van Wagenen, had a pinch-hit double to make it 10-8.

Suzuki’s eight-pitch at-bat ended with a 99.9-mph fastball flying over Nimmo’s head and landing a dozen rows deep in leftfield. That completed the largest ninth-inning-or-later comeback in Nationals/Expos franchise history.

“That team didn’t let up at any moment,” Diaz said through an interpreter. “I was throwing my pitches, I thought I was executing my fastball, my slider. It just happened to be that he got me. He was waiting on that pitch and he hit it out.”

Callaway said: “Man, it looks like Diaz’s stuff is electric. He’s throwing 99, he’s touching 100, and they just hit it. It’s tough.”

That turned everything else into a footnote. The third matchup of the year between Cy Young contenders Jacob deGrom (seven innings, four runs) and Max Scherzer (six innings, four runs) was a wash. Wilson Ramos extended his hit streak to 26 games, tied for second-longest in franchise history. Joe Panik hit his first homer with the Mets. Nimmo made a great diving catch in center.

The Mets left the ballpark Tuesday night about 14 hours before first pitch Wednesday. Callaway and deGrom offered the usual lines about turning the page and being resilient, and McNeil said the Mets have to pick each other up.

But some bad losses are worse than others.

“Just because we’re encouraging each other doesn’t make it feel any better,” Nimmo said. “You have to come to terms with that with yourself.”

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