MILWAUKEE -- The Mets wasted another stellar pitching performance, although it took an entire extra game to do it.

Ryan Braun singled in two runs after Chris Flexen walked the bases loaded in the 18th inning to give the Brewers a 4-3 victory over the Mets on Saturday, the longest game in Miller Park history in terms of innings.

“Overall as a pitching staff, we threw the ball great,” manager Mickey Callaway said. “I think the way guys stepped up, it was a heck of a job. There at the end, we just didn’t throw the ball over the plate. You give free passes, you’re going to get beat.”

Flexen, called up earlier in the day, escaped a two-on jam in the previous inning, but then he walked the bases loaded with one out. Braun then lined a 2-1 pitch through the right side for his sixth hit of the game.

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"It's absolutely a tough one,” Flexen said. “The team battled that hard to get all the way back. We take the lead, we go out there with momentum. To have a loss like that is a big letdown on my part. I failed to do my job."

The six hits were a career high for Braun, raising his average from .226 to .263.

“That’s a game you badly want to win because if you do win it, it feels like you won two or three games,” Braun said. “If you lose, it feels like you lost 10.”

The Mets took a 3-2 lead in the top of the 18th when Jeff McNeil singled home Adeiny Hechavarria with two outs.

Hechavarria, called up Friday from Triple-A Syracuse, singled with two outs in the 18th off Taylor Williams and stole second. McNeil then lined an RBI single to left.

After managing just three hits through eight innings, the Mets tied it 2-2 when Pete Alonso opened the ninth inning with his 10th home run, a 398-foot shot to right-center off Junior Guerra, who had not been scored on in nine of his past 10 appearances.

“This one really doesn’t sit well,” Alonso said. “This is a really tough pill to swallow. The positive light is that we got back in the ballgame. Our pitchers did an absolute hell of a job. Jeff came up clutch to put us there in the lead in the whatever-teenth inning it was, I think it was the 18th inning. That was a really good job by everybody, sticking in there, grinding every pitch out. It’s just really unfortunate to come up on the short end of this one.”

Amed Rosario's RBI triple in the second after a two-out single by Wilson Ramos accounted for the Mets’ first run off Gio Gonzalez, making his second start since being signed as a free agent on April 27.

Zack Wheeler, who struck out 10 in seven innings, was the latest to be hurt by a lack of support. Wheeler gave up two runs on three hits and a walk in the third inning, when the Brewers erased a 1-0 deficit. Seven relievers followed Wheeler with 10 scoreless innings.

“It was one of those games that you really want to win,” Wheeler said. “You battle through it and play hard. Tonight stinks, but I like the way our guys battled.”

Ramos made a huge play with two on in the bottom of the 13th, catching Eric Thames off first base for the second out.

The three runs were the most scored by the Mets in their past four games, giving them a total of five over that span. They won on Thursday when Noah Syndergaard backed his four-hit shutout with a solo homer for a 1-0 victory at Cincinnati. That came after the Mets had been blanked 1-0 the previous game.

Wheeler's errant pickoff throw contributed to the Brewers’ two early runs. Ben Gamel singled to open and advanced on Wheeler's throwing error. Wheeler struck out Orlando Arcia and Gonzalez, but Lorenzo Cain delivered an RBI single to right. Thames fell behind 0-2, before salvaging a seven-pitch walk. Mike Moustakas then lined a 1-2 pitch to right for a run-scoring double.

Matt Albers followed Gonzalez with 1 2/3 scoreless innings. With hard-throwing Josh Hader unavailable after a two-inning save in a 3-1 victory on Friday, the Brewers turned to Guerra in the eighth.

“It’s going to be challenging the next few days,” Callaway said. “Like I said earlier, anytime you play 18 innings, it puts you in a bit of a bind. They have to come out and play the same game we have to play tomorrow.”