Wilmer Flores of the Mets celebrates his ninth inning walk...

Wilmer Flores of the Mets celebrates his ninth inning walk off home run against the Milwaukee Brewers at Citi Field on Sunday, Apr. 15, 2018. Credit: Jim McIsaac

When he stepped to the plate in the ninth inning Sunday, Wilmer Flores was like everybody else at Citi Field: cold and ready to go home.

Only Flores, however, had the ability to unbreak the tie and end the game — and he did. He swatted a two-out home run to left-centerfield to give the Mets a 3-2 win over the Brewers.

The Mets, a National League-best 12-2, have opened a season with five straight series wins for the first time. The fact that they ended the game just before a cold rain descended upon Flushing made it even better.

“That’s what we were saying when they came off the field: Win it right here and we get to go get warm,” manager Mickey Callaway said. “I know the players were ready to get off the field.”

Said Flores: “We didn’t want to play extra innings, for sure.”

After the team mobbed Flores at home plate, Yoenis Cespedes gave him the customary Gatorade bath, complete with ice.

“I told him no,” Flores said. “But he still did it.”

Flores saved the Mets from having to go to extra innings with a thin bullpen. As Flores batted, Seth Lugo — the last available reliever, unless Callaway wanted to go to Paul Sewald (three innings, 48 pitches on Saturday) again — warmed in the bullpen.

Callaway mixed and matched from the sixth inning on after Noah Syndergaard lasted only 5 1⁄3. Through 14 games, Jeurys Familia (10 innings), AJ Ramos and Jerry Blevins have pitched in nine each. Robert Gsellman also pitched Sunday and is up to eight games (8 1⁄3 innings).

“We haven’t overtaxed our bullpen yet, and we’ll try not to,” Callaway said. “At some point, we’re going to have to start doing the game where we send some guys out and bring some guys up. But we really can’t do anything about it. You have to win games.”

Syndergaard repeatedly flashed his dominance but again was inefficient, throwing 101 pitches, his most in almost a year. He was charged with one run (which was unearned), struck out 11, including eight in a row, and walked one.

Hernan Perez had Milwaukee’s first hit, a leadoff single to left in the fifth that ended the strikeout streak. Syndergaard matched Jacob deGrom (September 2014) for the second- most consecutive batters struck out by a Met. (Tom Seaver owns the major-league record with 10 in a row, in April 1970 against San Diego.)

Syndergaard’s greatest adversity came during a 10-pitch walk to Lorenzo Cain during a 29-pitch first inning. That set him back on his pitch count for the rest of the day, and he needed 90 to get through five.

“I feel like I didn’t even really break a sweat out there, to be honest,” Syndergaard said. “I kept things calm, cool and collected. Really free and easy out there. I feel like I had plenty of stamina left.”

The run charged to Syndergaard came on an error after Gsellman replaced him. Shortstop Amed Rosario made a diving stop of a grounder but his throw to first was off the mark, allowing two unearned runs — one of Syndergaard’s, one of Gsellman’s — to score.

The Mets scored against Jhoulys Chacin (four innings, one run) in the first inning on Todd Frazier’s single to left.

Brandon Nimmo hit his first homer of the year to tie it in the sixth. Always quick to get down the line, he had rounded first by the time the line drive landed in the rightfield seats. Nimmo went 3-for-5 and was a double shy of the cycle before striking out in the eighth.

“In the moment, I didn’t really know,” Nimmo said. “As I was getting up there, everybody was saying, ‘Uh, hit a double.’ And I was like, ‘OK.’ That would have been awesome.”