There was the crack of the bat, followed by a collective gasp. Then came a couple seconds of anxious waiting to see if this line drive had enough to clear the wall.

When the ball landed in Atlanta’s bullpen, the Citi Field crowd of 39,748 roared as they realized history had been made early in Tuesday night’s 13-5 win: Pete Alonso stood alone as the Mets’ home run king.

Alonso crushed career homer No. 253, breaking his tie with Darryl Strawberry atop the franchise’s career home run list, on righthander Spencer Strider’s first-pitch, 95.1-mph fastball down the middle.

The two-out, two-run homer — which was hit 112.8 mph off the bat and traveled 394 feet to right-centerfield — gave the Mets a 5-1 lead in the third.

“As a kid, you don’t really think that it’s in the realm of possibility to be a franchise home run leader,” Alonso said. “You just don’t. You just want to get to the big leagues and give it your best. And the dream is really kind of this opaque and unknown thing, and you just want to get there and compete, play for a World Series, play winning baseball.

“But to have that opportunity, you really don’t think about [it]. It’s a wild dream, to be honest. It’s really special.”

Clay Holmes subsequently squandered the four-run cushion as Atlanta tied it in the fourth, but he was bailed out by the Mets’ bats. They exploded for six homers and 16 hits in a blowout win on a celebratory night. All 13 runs came with two outs.

Alonso (3-for-5, three RBIs) added home run No. 254 for good measure in the sixth, a solo shot that gave the Mets an 11-5 lead.

“He didn’t want to make tonight about Pete Alonso, so he wanted to make it about the team and the fact that we got the victory,” Carlos Mendoza said. “But overall, enjoyed it. I was a fan. I had tears in my eyes.”

Francisco Alvarez went 3-for-4 with two homers and four RBIs. Brandon Nimmo, Starling Marte, Cedric Mullins and Brett Baty each had two hits. Justin Hagenman pitched a hitless final four innings for his first career save.

The Mets (64-55) snapped a seven-game losing streak and moved within five games of the NL-East leading Phillies (69-50), who lost to the Reds, 6-1.

Alonso first hugged Nimmo, who scored on the record-setting homer, and then Jeff McNeil, who was on deck. He took off his helmet for a curtain call before being greeted by the entire team outside the dugout.

“It meant a lot, even though he won’t say it,” Mendoza said. “But you watch that face and how much joy he had, especially when he stood on the bench in the dugout and just tipped his helmet to the crowd. He’s like a kid with a new toy. He was humble. It was just hard to describe the face of Pete. He was just enjoying the whole moment.”

Alonso tied Strawberry in Saturday’s 7-4 loss to the Brewers. Alonso has played 965 career games, all with the Mets. Strawberry played 1,109 games for the Mets before signing with the Dodgers as a free agent.

“I just want to say congratulations on breaking the home run record,” Strawberry said in a video message posted by the Mets on X. “Listen, you have worked hard. You have stood up in the pressure of New York City, and you have played well and it’s well deserved. You are a homegrown player. And again, congratulations, and continue to have great success. All the best, buddy.”

Holmes’ fourth-inning implosion temporarily deflated the euphoric energy inside Citi Field.

Nacho Alvarez Jr. hit a two-run double, Jurickson Profar drove in a run on a fielder’s choice and Matt Olson tied it at 5 with an RBI double for Atlanta (51-68).

Holmes allowed five runs, six hits and five walks in a season-low-tying 3  2⁄3 innings, striking out four.

Luckily for Holmes, the Mets offense showed up in a huge way.

The Mets took an 8-5 lead in the fourth on a three-run homer by Nimmo, who was 0- for-his last 19 entering Tuesday. They added two more in the fifth on Alvarez’s RBI double and Baty’s RBI single.

Strider allowed eight runs and eight hits in four innings.

After Alonso’s sixth-inning homer, Alvarez — whose second-inning two-run homer gave the Mets a 3-1 lead — and Baty launched back-to-back solo shots for the game’s final runs.

“It’s unimaginable,” Alonso said. “I mean, it’s still really not fully set in, and I don’t think I’m fully going to appreciate this moment until the offseason.”

Notes & quotes: Frankie Montas will be moved to the bullpen. Mendoza said that top righthanded pitching prospects Nolan McLean and Brandon Sproat are both “in the conversation” to pitch Saturday.

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