The Mets didn’t have one more final stirring comeback in them this weekend against Washington’s maligned bullpen.

Two runs against their Seth Lugo-less relief corps in the seventh and Victor Robles’ two-run homer against still-shaky Edwin Diaz in the ninth were too much to overcome Sunday as the Mets failed to complete a three-game sweep of the Nationals. Their 7-4 loss in another energetic atmosphere at Citi Field halted their eight-game winning streak entering Tuesday’s visit to first-place Atlanta.

The Mets, winners of 15 of their previous 16 games since July 25, also squandered their first chance to overtake Washington for second place in the National League East and in the NL wild-card standings.

“It’s unfortunate that we fell short today, but I mean, hell, we were on an eight-game win streak. It was really special,” said Pete Alonso, who was charged with a three-base, three-run error in the first inning on a wild throw past Jacob deGrom at first base for a quick 3-0 hole. “We haven’t lost since [Aug. 2 in] Pittsburgh, so that’s pretty damn good.

“I think regardless of today, we have a ton of momentum going into this road trip and I’m really excited. I just need to turn the page and get better and be ready to play in Atlanta.”

The Mets now sit a game behind the Cardinals for the second wild-card spot, with the Brewers a half-game back of St. Louis.

Other than three unearned runs scoring on that one crazy play in a laborious 34-pitch first inning, deGrom was typically stingy — permitting no earned runs — but he lasted just five frames on 101 pitches before turning over a 3-3 knot to Luis Avilan in the sixth. The reigning Cy Young Award winner lowered his ERA to 2.68 overall and 1.97 over 15 starts since May 22.

The Mets, who seized Friday’s series opener with four runs in the ninth inning and then won the following night with two in the eighth, roused the crowd of 41,000 once again in clawing back to even the score with three runs against Nats starter Anibel Sanchez in the second. Joe Panik recorded his first RBI in three games with the Mets and Jeff McNeil plated two more runs with his first of two doubles.

With the dependable Lugo unavailable after recording the final six outs Saturday night, however, the Mets (61-57) fell behind again on ex-mate Asdrubal Cabrera’s two-run double with the bases loaded against lefty reliever Justin Wilson (inherited from Robert Gsellman) in the seventh.

Michael Conforto recouped one run with a sacrifice fly in the bottom half to score McNeil, who had opened the inning with a double off the wall in right-center.

After Wander Suero worked a scoreless eighth for the Nats, Diaz surrendered a two-run blast to left on a flat 2-1 slider to Robles, who had entered the game in the seventh as an injury replacement for Juan Soto, for another three-run deficit.

“I try to have a positive attitude every single time, I’m just trying to get out of this rough stretch that I’m in right now,” Diaz said through a translator. “If I’m frustrated all the time, it’s just going to get worse. Every single time I’m on the mound, I just try to get better.

“In order for me to have better outings, I need to execute my pitches.”

Robles’ blast was the 11th home run yielded this season by Diaz, six more than he allowed in all of 2018 with Seattle. But with few reliable arms in the bullpen, Mickey Callaway acknowledged he still “can’t really afford to” remove Diaz entirely from high-leverage situations.

“He’s gonna continue to get big outs for us and continue to pitch in big games,” Callaway said. “Like we did [Saturday] night, we’ll pick our spots [with Lugo] and do our best to win a game every single night.”

The Nationals (62-55) certainly can commiserate. Sean Doolittle coughed up all four runs in Friday’s ninth inning and entered with a 15.00 ERA in seven appearances against the Mets this season. But provided extra cushion from Robles’ homer, the lefty closer tossed a scoreless ninth for his 26th save.

Can’t blow ’em all, can’t win ’em all, indeed.

“Getting this series win was huge for us,” Alonso said. “Granted, we had an opportunity to sweep and it’s unfortunate that we didn’t. But we played some really quality baseball this weekend. I don’t think there’s any doubt about that.”