PITTSBURGH — Jordy Mercer knows the routine. He figured it was time he experienced it for himself.

The Pittsburgh Pirates second baseman singled up the middle off Gonzalez Germen with two outs in the 11th inning to send teammate Andrew McCutchen sprinting home with the winning run in a 3-2 victory over the New York Mets on Friday night.

Mercer celebrated the first walkoff hit of his career and the sixth of Pittsburgh’s stunning season by flipping his bat in the air and then running for safety.

“You make them chase you down because you know you’re going to get punished afterward, punched and stuff,” Mercer said. “It’s all worth it in the end, though.”

McCutchen led off the 11th with a walk, stole second and then easily beat the throw home from center fielder Juan Lagares to end the Mets’ four-game winning streak.

The Pirates stayed one game behind St. Louis in the tight NL Central race.

Vin Mazzaro (5-2) retired all three batters he faced to earn the victory. Starling Marte had two of Pittsburgh’s six hits, and Pedro Alvarez added his 24th home run.

Mets All-Star David Wright had two hits and extended his hitting streak to 12 games. He had an RBI single but also flied out with two runners on to end the New York 10th. Kirk Nieuwenhuis hit his third homer of the season for New York.

Germen (0-1) got only two outs in his first inning in the majors and took the loss. He struck out Alvarez and Gaby Sanchez with McCutchen on second before Mercer’s grounder slipped by shortstop Omar Quintanilla and into the outfield.

“He made some great pitches, too,” Mets manager Terry Collins said of Germen. “The 3-1 pitch to Gaby Sanchez was about as (gutsy) of a pitch that you’ll ever see.”

The game carried a little more heat than usual between one team in the midst of a pennant race and another rebuilding.

Wright, the starting NL All-Star third baseman and Home Run Derby captain, added Alvarez to the NL’s derby roster on Thursday after Colorado’s Carlos Gonzalez pulled out because of a hand injury.

Still, Wright’s perceived initial snub of Alvarez wasn’t forgotten by Pirates fans. He was booed lustily before each at bat, even though he and Alvarez — who will make his All-Star debut — exchanged a handshake and a brief chat before the national anthem.

“They’re knowledgeable fans, they know what’s going on and it’s cool that they’re upset and passionate about it,” Wright said. “It made for a nice atmosphere.”

Alvarez wasted little time celebrating. One batter after Jose Tabata reached on an infield single in the bottom of the first, Alvarez hit the first pitch he saw from Jeremy Hefner into the New York bullpen in center field. He trotted past Wright without looking up as the seventh sellout crowd of the season roared.