NEW YORK -- For weeks now, the Mets have flitted about .500, keeping that mark close but never exceeding it. They haven’t been above .500 since May 2, more than a month ago. They have struggled to gain the momentum necessary to move up the NL East standings.

So it was Tuesday afternoon, when the Mets took an early three-run lead at Yankee Stadium with a chance to move back to .500 for the first time since May 28. Then, through a combination of sloppy defense and extra-base hits, they melted down in the middle innings of a 12-5 loss to the Yankees. Zack Wheeler allowed a career-high nine runs (five earned), falling two short of the franchise record for a single game.

• Box score

“It’s like that mark, you get up to it and you get knocked back down,” manager Mickey Callaway said. “But we’re not going to give up. We’re going to get to .500 and then we’re going to take off at some point. We’re just going to keep grinding away.”

The Mets went on to salvage a split with the Yankees behind another solid outing from Jason Vargas in the nightcap.

Facing a playoff-caliber Yankees team, the Mets gave their interborough rivals multiple extra outs and scoring chances in Game 1. It began in the third, after Jeff McNeil hit a three-run homer off Masahiro Tanaka to give the Mets a three-run lead. In the bottom of the inning, with Brett Gardner on first base, DJ LeMahieu hit a comebacker that Wheeler fielded and fired to second base. Amed Rosario caught the throw but never touched the bag, allowing Gardner to reach safely and, eventually, to score on Gary Sanchez’s RBI single -- a bloop hit just out of McNeil’s reach in shallow right.

“It was a tough one to swallow,” Wheeler said. “I made some pitches when I had to. They also hit some good pitches and I left some balls over the plate. … I was pretty frustrated out there, but what are you going to do?”

An inning later, Gio Urshela and Luke Voit both homered during an inning that Todd Frazier extended with a throwing error. And in the fifth, Kendrys Morales doubled just out of the reach of J.D. Davis, a natural infielder forced recently to shift his position to left. The Mets and Yankees combined to commit five errors in the game.

“I’ve got to make a better throw,” Frazier said. “Slow ground ball, I had plenty of time. Once I threw it, I knew it was going in the wrong direction. So that was on me. It turned into a bigger inning because I couldn’t get the ball to first base, bottom line.”