Yoenis Cespedes broke stride as if his muscles had suddenly frozen on the way to second base. Moments later, his hands rested on his knees, his left hamstring seized in pain, and a cloud of doubt rose menacingly over Citi Field.

To this point, the Mets’ horrendous start had merely been reflected in the standings in the form of wins and losses. But on a tortured Thursday afternoon, that misfortune gained a face, one that was twisted into a knot of worry.

It belonged to Cespedes, the most dynamic player on a talented team that has crashed to last place. The descent was made official by a 7-5 loss to the Braves, a defeat that punctuated an exceptionally wrenching day that featured physical pain, mental strain and needless self-sabotage.

“From what I saw, I don’t know of anybody coming back in 10 days walking off like that coming off the field,” said manager Terry Collins, who stopped just short of announcing that Cespedes would be going on the disabled list with a strained left hamstring.

Meanwhile, biceps tendinitis scrubbed the scheduled start of staff ace Noah Syndergaard. And replacement starter Matt Harvey did not hear until 10 a.m. that he would get the assignment. That’s despite the fact that Syndergaard’s arm issue had been on the Mets’ radar since earlier in the week.

“I had no idea,” said Harvey, who thought he’d have a rest day after an intense workout and throwing session the day before.

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Predictably, a weary Harvey got shelled, his performance blending into the general malaise that has engulfed the Mets. They have lost six straight and 10 of 11. At 8-13, they’re in last place in the NL East.

With the exception of losing on Opening Day last year, the Mets hadn’t skidded into the basement since June 27, 2014.

“We know we’re going to be better than this,” said Jose Reyes, though the Mets face a brutal challenge ahead.

The Mets had hoped to salvage a homestand in which they have played their worst baseball since becoming contenders in 2015. A lack of energy even prompted Collins to address the team following the loss. During his speech, he offered a reminder that last year’s team made the playoffs while overcoming injuries of their own.

“We still made it through,” said Collins, who noted a lack of energy. “We can do that again. But it’s got to start now.”

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Harvey looked unprepared, chased after allowing six runs on five hits in 4 1/3 innings. His mechanics looked sloppy, costing him in command and velocity.

Harvey, who is coming off thoracic outlet surgery, walked three batters in an inning for the first time in his career. It happened in the second, when the Braves took a 2-0 lead that seemed insurmountable.

“It’s hard to win a ballgame like that,” Reyes said. “You go down 2-0, 1-0, and you feel like you already lost. As a baseball player, when you have that attitude, that’s bad.”

The Mets tied it in the fourth, a rally that began with the double that ultimately sent Cespedes from the game. But the Braves scored four runs in the fifth, the biggest blow coming on a three-run shot from Kurt Suzuki.

It came after Collins intentionally walked Nick Markakis, yet another decision gone bad. He was hardly the only guilty party.

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First-year third base coach Glenn Sherlock stunted a potential Mets rally in the second when he sent Jay Bruce home on a Neil Walker single, challenging cannon-armed centerfielder Ender Inciarte. Bruce was thrown out by 15 feet.

Reyes cost the Mets a run in the second. With the bases loaded, opposing pitcher R.A. Dickey hit a roller to Reyes, who had plenty of time to force the plodding Suzuki at home. Instead, Reyes threw to first.

So it went for the Mets, who must now deal with another questionable decision.

Cespedes initially hurt his hamstring while running the bases last Thursday against the Phillies. The Mets chose not to place him on the disabled list. Instead, he rested three games, returned without incident Wednesday night, then needed assistance going down the steps as he departed on Thursday.

It’s an image that will linger if this stretch indeed proves to be the early undoing of a season filled with expectations. Now, the Mets arrive in Washington on Friday for a three-game series against the surging Nationals. They could be without Syndergaard and they’ll be without Cespedes, who was sent to the hospital after the game.

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Said Reyes: “We’re going to see what we’re made of.”