By the end of a horrendous evening, the Mets had not merely played down to their competition. No, they had done much worse.

In nine brutal innings, littered with carelessness and recklessness, the Mets fell, 4-3, to the cellar-dwelling Braves, offering a reminder of just how precarious this season of promise has become.

The mistakes piled up like firewood but the Mets did not lose ground to the Nationals, who lost in San Diego.

Wilmer Flores, the tying run in the ninth inning, was cut down at the plate because of an overzealous send by third-base coach Tim Teufel.

An inning prior, the Braves’ Ender Inciarte caught Curtis Granderson making a half-hearted throw back to the infield, tagging up and advancing to third on a liner. Inciarte later scored the go-ahead run on a pitch in the dirt.

And as if the loss wasn’t enough, starting pitcher Steven Matz was pulled after allowing two runs in six innings with tightness in his elbow and reliever Jim Henderson walked off the mound with an impingement in his shoulder.

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Matz insisted he was dealing with normal soreness and Henderson said initial strength tests were encouraging. But when it comes to health, little has gone right in a season marked by injuries.

“This is a tough one, especially with what’s going on right now, with a bunch of guys down,” manager Terry Collins said. “You can’t lose these kind of games. You’ve got to win these games. You’ve got to win these games that you have opportunities to win. When times are tough, these are big games.”

The Mets blew a 3-0 lead. They finished 0-for-8 with runners in scoring position and stranded seven runners. The most egregious missed chance came in the ninth.

Flores reached base to start the frame when Braves shortstop Erick Aybar got handcuffed on a grounder. James Loney followed by ripping a double to the gap in left-center. In the coach’s box, Teufel waved home Flores, perhaps the slowest position player on the team. The relay beat Flores easily.

Said Collins: “We can’t get him thrown out in that situation.”

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Teufel slumped his shoulders and kicked the grass, his folly immediately clear. Later, the Mets did not make him available for comment.

Loney advanced to third base on a wild pitch and Alejandro De Aza got plunked, giving the Mets once last fleeting sense of hope. But with the winning run on base, Granderson struck out looking, cementing a night of failure that turned on his own defensive miscue.

After Inciarte doubled in the eighth, Jeff Francouer hit a liner to Granderson, who caught it but took his time throwing the ball back to the infield. When he did, he made only a half-hearted toss.

Presented with an opening, Inciarte bolted for third.

“Inciarte, you’ve got to give him credit. He made a head’s up play,” Granderson said. “He was alert and was able to advance to third. If I give Neil [Walker] a better throw . . . Neil has a better shot at getting him out at third base.

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“You never know. He’s a speedy guy. He might have still tried to be aggressive in that situation.”

Inciarte completed his trip when Addison Reed bounced a pitch in the dirt, forcing Rivera to scramble for it. They reached the plate at the same time. But Inciarte emerged from a cloud of dirt safe, his face revealing an adrenaline-fueled dash around the bases that left the Mets stunned.

“It’s a part of the game,” Rivera said. “You want to block every ball.”

Now, the Mets must hope that their injury count doesn’t pile up.

Matz said his elbow was “just a little tender” after throwing 99 pitches, but he chalked it up to typical fatigue, unlike the pain that prompted the Mets to skip a start last month.

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Meanwhile, Henderson hoped the “discomfort” in his shoulder would keep him out of action for only a day or two. But the red flags were clear.

Henderson averaged just 91 mph on his fastball, including the one that Tyler Flowers bashed for a game-tying homer in the seventh inning.

Said Henderson; “Structurally, hopefully, it seems like everything’s good in there.”