Pete Alonso hits 41st homer, but Edwin Diaz is hurting as Mets lose to Braves  

So much of the Mets’ improbable run to playoff contention this summer has been marked by comebacks that have felt inevitable, with signature moments by star players, the kind that can live long in franchise lore if this hot streak turns into something bigger.

Most of Saturday stuck to that script for the Mets. Pete Alonso’s go-ahead homer in the fifth was his 41st of the season, tying the franchise single-season record, and he said he “couldn’t have dreamt it up any better.”

And then everything fell apart for the Mets, who lost to the Braves, 9-5. At 67-62, they are two games back of the second National League wild-card spot.

Zack Wheeler allowed the Braves to tie it a half-inning after Alonso’s blast, a lackadaisical play by J.D. Davis helped Atlanta build a lead and the Mets’ bullpen — good lately — allowed four runs in three innings.

The unfortunate series of events ended with closer Edwin Diaz — suffering what the Mets described as a tight trapezius muscle in his neck and back — walking off the mound with head athletic trainer Brian Chicklo.

Diaz wanted to keep pitching and hadn’t experienced this before, Mickey Callaway said. He will be re-evaluated Sunday.

“When I was warming up, I was feeling a little bit uncomfortable in my neck area,” Diaz said through an interpreter. “I thought I could loosen it up eventually, but it just tightened up when I was pitching.”

Diaz allowed a homer to Freddie Freeman, struck out Josh Donaldson and walked Charlie Culberson before Callaway and Chicklo visited the mound. Those struggles — and the injury, which seems to be minor — frustrated Diaz, who has a 5.55 ERA and hasn’t been able to keep much positive momentum in recent months.

“I don’t understand why it happened,” Diaz said. “[Friday] I felt good. When I felt like I was starting to finally get it going, and something like this happens.”

The Mets’ problems began long before Diaz entered. In the sixth, Francisco Cervelli (3-for-5, three RBIs) chopped a grounder down the leftfield line, ruled a two-base error on third baseman Todd Frazier. Rafael Ortega’s single tied the score.

Wheeler allowed five runs (four earned) in six innings, his third dud of a start in a row. “It’s just inconsistency,” he said. “I’m trying to figure it out myself. I don’t know. The last bullpen [session] I threw was probably the best one of the year. Not to see it translate was very frustrating.”

Jeff McNeil led off the seventh with a pinch-hit double, but after Amed Rosario failed to get a sacrifice bunt down, he sent a grounder to shortstop Adeiny Hechavarria, who threw to third to get McNeil.

“It was probably a pretty good, aggressive play [by McNeil],” Callaway said. “And then an outstanding job by the shortstop.”

Rosario was erased, too, when he was caught stealing second. Hechavarria made a smooth grab of Cervelli’s throw on the third-base side of the bag and tagged Rosario.

Atlanta (79-52) took the lead on Ronald Acuña Jr.’s two-out single in the eighth. With runners on first and second, he sent a line drive to left-center. Ortega scored easily from second, and Billy Hamilton, perhaps the fastest runner in the majors, sped home from first as Davis lobbed the ball back to the infield.

Davis said he was going to throw to third, but Hamilton already was almost there. Then he looked to first, where Acuña had taken a big turn. Hamilton scored easily on Davis’ no-urgency throw to Rosario.

“That’s my fault,” Davis said. “I should be throwing into Rosie right away instead of picking up the runner at first.”