ARLINGTON, Texas — The ball took off high into the Texas sky, its hang time giving the beleaguered man on the mound plenty of time to seethe. Once the arcing drive cleared the rightfield fence, the pitcher shook his head, gritted his teeth, and punched the inside of his empty glove.

Jacob deGrom’s night would be over soon.

Such has been the fate of the Mets, who have been undone by what was supposed to be their strength. In a 10-8 loss to the Rangers Tuesday night, deGrom looked like just another mere mortal after Joey Gallo’s towering third-inning homer, a moment of weakness in a season that has been defined by them.

“Bad outing,” deGrom said after getting punished for leaving pitches down the middle. “That’s on me again. Gotta be better than that.”

The Mets (24-32) lost for the fifth time in six games, falling to eight games under the .500 mark for the first time since Sept. 6, 2014. This was the fallout after the Mets’ de facto ace get battered into submission, a meltdown that only deepened questions about a crumbling starting rotation.

By the time he walked off the field for good after the fourth, deGrom had tied a career-high by allowing eight earned runs. It came on 10 hits, including a pair of homers. He walked one but struck out just two.

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“It’s definitely not fun,” said deGrom, whose ability to pitch without his best stuff has suddenly escaped him. “It’s just a poor job on my part.”

Three times, the Mets gave deGrom a lead. Three times, he gave it back. The Mets got homers from Juan Lagares, Asdrubal Cabrera and Neil Walker to build a 4-3 advantage in the third off one-time Mets righty Dillon Gee. But the Rangers scored seven unanswered runs, enough to hold off a furious rally in the ninth.

The Mets got back-to-back homers from Curtis Granderson and Travis d’Arnaud, slicing the deficit to two runs. But the comeback stalled when Asdrubal Cabrera struck out and Jay Bruce hit into a game-ending double play.

For the seventh time this season, Mets pitching allowed an opponent to reach the double-digits. It happened only six times last season and four times in 2015, when dominant pitching pushed the Mets to the World Series.

Nomar Mazara’s solo shot capped a three-run fourth inning that proved to be deGrom’s last. He departed trailing 8-4.

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In the dugout afterward, manager Terry Collins threw his arm around a dejected deGrom, the owner of a 4.75 ERA that wasn’t helped by a sloppy defense behind him.

“The two seamer’s not working right now, and he’s leaving balls right in the hitting area,” said Collins, who wanted to offer his struggling pitcher some reassurance.

It wasn’t that long ago when it appeared that the righthander had gotten himself on track. On May 26 against the Pirates, deGrom allowed one run in 8 1⁄3 innings, a 118-pitch effort that was easily his best outing in his first season since surgery to repair a nerve problem in his elbow.

In two starts since, deGrom has surrendered a staggering 15 earned runs and 18 hits. Physically, he insists he feels fine, only adding to the frustration of the results.

Now, the Mets find themselves with another malfunctioning arm at at a time when they are considering a six-man rotation with Steven Matz and Seth Lugo set to rejoin the rotation.

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“Maybe, the extra day will help these guys be a little bit sharper and get deeper into the game,” Collins said. “These guys have all pitched better with an extra day.”

Indeed, after Thursday’s off day, the Mets have 18 games in 17 days. An extra starter could make the stretch easier to navigate. But it won’t matter unless deGrom gets back on track to anchor the rotation.

On Tuesday, the Mets did what would have once been unthinkable. They bashed five homers and banged out 17 hits to score eight runs against the Rangers. And with deGrom on the mound, they lost.

Said Collins: “We’ve got issues we’ve got to deal with.”