Phillies first baseman Rhys Hoskins scores on an RBI single as...

Phillies first baseman Rhys Hoskins scores on an RBI single as Mets catcher James McCann goes airborne before he can make the tag during the eighth inning on Monday in Philadelphia. Credit: AP/Laurence Kesterson

PHILADELPHIA — The Mets had to wait four extra days for their first game of the season. They’ll have to wait at least one more for their first win.

For all that is different about these Mets under new owner Steve Cohen, their new era began with the same major themes from the recent past: Jacob deGrom absolutely dominating, the bullpen absolutely not, the lineup providing him a modicum of support and the defense not helping when it matters most.

Those narratives collided in a 5-3 disaster of a loss to the Phillies on Monday, the feel-good vibes of Opening Day dissipating with the eighth-inning lead.

A rally in the ninth, including Francisco Lindor’s first hit with the Mets (a single), brought the potential go-ahead run to the plate with two outs. But Pete Alonso flied out to the wall in rightfield, ending the game.

"This one," deGrom said, "got away from us."

Added Trevor May: "It’s frustrating. I can’t imagine what it was like to watch it."

The culprits this time: the righthanded May and lefthanded Aaron Loup, the Mets’ only major-league offseason additions to a bullpen that has been bad for years.

Tasked with the eighth inning in his Mets debut, May retired one of four batters and left the bases loaded. He yielded to Loup, whose first assignment was Bryce Harper.

Loup hit Harper with a pitch, forcing in a run and cutting the Mets’ two-run lead in half. J.T. Realmuto — the catcher the Mets passed on signing in favor of James McCann in December — tied it with an RBI single to left. When Alec Bohm sent a grounder to third, Luis Guillorme, a surehanded defensive replacement, threw wide to home, allowing two runs to score and granting the Phillies their first lead of the night. Didi Gregorius capped the five-run inning with a sacrifice fly.

"We know the result wasn’t the one desired, but we liked the guys that had the ball," manager Luis Rojas said. "It was the only bad inning we had in the game."

Loup said: "You want to come out and make a good impression. It definitely sucks. Hitting the first batter is what started it all."

That negated deGrom’s great night. He finished six scoreless innings on just 77 pitches, well short of the 100-pitch limit prescribed for him by Rojas before the game. Rojas said he, deGrom and the pitching coaches agreed to pull deGrom because it had been 10 days since he pitched.

"If that was Thursday (the Mets’ original Opening Day) and I was on normal rest, I don’t think there’s any chance I’m coming out of that game," deGrom said.

The Phillies’ Harper said, "We were happy as a team, of course, getting one of the best pitchers — if not the best pitcher — in the entire world out of the game."

DeGrom’s fastball averaged 99.1 mph. He retired his final nine batters, struck out seven, walked two and scattered three hits — and went 2-for-3 with an RBI as a hitter.

"Jake shouldn’t have to do everything himself," May said. "That’s not what teams are. And frankly, he did almost everything today."

An early inflection point: Kevin Pillar’s fourth-inning at-bat with the bases loaded and one out. He hit leadoff in place of Nimmo — and played the outfield in place of Dominic Smith — because the Mets were facing a lefthanded starter in Matt Moore, Rojas explained before the game.

But by the fourth, Moore (two runs, 3 1/3 innings) was out and righthander Brandon Kintzler was in. Smith remained on the bench. Pillar grounded into a double play.

"We did talk about it briefly," Rojas said of using Smith, noting that he was "satisfied" with the Mets’ process. He later added, "We were thinking Pillar was actually going to come through for us."

Smith never got into the game.

"I know the fans are disappointed, I know everyone is disappointed," May said. "But there are 161 [games] left."

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