Chad Green of the Yankees walks to the dugout after the...

Chad Green of the Yankees walks to the dugout after the sixth inning against the Mets in Game 1 of a doubleheader at Yankee Stadium on Friday. Credit: Jim McIsaac

The Yankees officially are a mess.

Their bullpen, mostly a strength in this oddest of seasons, suddenly is struggling — and it is proving very costly for the Yankees, who already had enough problems.

After Chad Green blew a three-run lead in a 6-4 loss in the first game of Friday’s doubleheader against the Mets, Aroldis Chapman allowed a walk-off two-run homer by pinch hitter Amed Rosario, sending the Yankees to a 4-3 setback and their seventh straight loss.

That followed Game 2 of Wednesday's doubleheader against the Braves, in which Green blew a one-run lead by allowing a two-run homer by Freddie Freeman.

Inheriting a two-on, none-out situation from Jordan Montgomery in the sixth inning of the first game, Green flushed it by allowing three home runs — a tying three-run blast by Pete Alonso and back-to-back two-out shots by Dominic Smith and Jake Marisnick.

“We just have to start finishing games off,” Aaron Boone said afterward. “It’s obviously a little bit tough for us right now.”

It appeared as if the Yankees (16-13), now four games behind the AL East-leading Rays and a half-game ahead of the third-place Blue Jays, would stop their losing streak in the nightcap, but Chapman, who had not pitched in 11 days, could not hold on.

Jonathan Loaisiga pitched a solid three innings as the opener in the second game, allowing one run and three hits and striking out three in three innings. The Yankees scored three runs in the third off lefthander David Peterson, with Erik Kratz, Aaron Hicks and Gary Sanchez each driving in a run. Nick Nelson allowed a run in the fifth to make it 3-2 and Luis Cessa’s scoreless sixth got the ball to Chapman.

The closer walked Jeff McNeil to start the seventh and pinch runner Billy Hamilton stole second. Rosario got ahead 2-and-0 before sending the next pitch over the leftfield wall to win it (the Mets were the home team in Game 2).

It's not every day that the ''home team'' has to watch the ''road team'' celebrate a walk-off victory, but that's what happened.

“It’s not fun,'' Clint Frazier said, "but luckily, we have one tomorrow and two the next day, and hopefully we can get back on track because we definitely need it right now.”

“At the end of the day, we have great players,'' reliever Adam Ottavino said. "We’ll get on a roll. Hopefully get a streak going in the other direction.”

Given that Freeman had hit a go-ahead two-run homer off Green in the righthander's most recent appearance Wednesday — meaning he had allowed four home runs in a span of seven batters and blown two leads in consecutive losses — Green's difficulties took headline status for the futile day.

“That’s going to happen over the course of the season, even with the best of relievers like Greeny,” Boone said between games (the start of the second game was delayed about 1 ½ hours by rain).

After allowing back-to-back singles by J.D. Davis and Michael Conforto to start the sixth, Montgomery turned a 4-1 lead over to Green. He promptly caught too much of the plate with a full-count fastball that Alonso put on the netting overhanging Monument Park for his sixth home run and a 4-4 tie.

Green then retired two straight before allowing back-to-back homers by Smith into the Yankees' bullpen and Marisnick into the leftfield stands to make it 6-4.

Montgomery was charged with three runs (two earned) and five hits in five innings-plus. The lefthander struck out six and did not walk a batter.

“Surprising just because of how dominant he’s always been,” Montgomery said of Green. “But nobody’s perfect. Doesn’t change my mind; he’s still one of the best relievers in baseball. It’s going to happen.”

Before Wednesday, Green had posted a 0.71 ERA in his first nine appearances, striking out 17 and walking four in 12 2/3 innings.

Dellin Betances, a career Yankee until the Mets signed him to a free-agent deal last offseason, hit Frazier with a pitch and walked Brett Gardner with two outs in the sixth but retired Sanchez on a fly to center. Edwin Diaz then struck out the side in the seventh, giving Mets pitchers 13 strikeouts.

Green’s struggles overshadowed what had been standout days by Frazier and Luke Voit.

Frazier, batting second in a lineup again missing Aaron Judge and already without the injured Gleyber Torres, DJ LeMahieu and Giancarlo Stanton, had an RBI double and a two-run homer to improve to 11-for-32 since being recalled Aug. 12. Voit, hitting leadoff for the second time in his career, went 3-for-4 and scored two runs. Frazier’s RBI double highlighted a two-run first and his two-run homer in the second brought in Voit to make it 4-0.

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