The Mets popped the champagne at Brew City on Thursday night — and had an extra lucky charm.

After trailing for a long time, the Mets went wild in the clubhouse, popping champagne in celebration as they secured a spot in the NLDS with a wild 4-2 victory over the Brewers.

Pete Alonso, the Game 3 hero who led the Mets into the top of the ninth with a dramatic three-run home run, was at the center of it all with an unusual piece of playoff lore.

A Wisconsin pumpkin.

Speaking to reporters in the rowdy scene in the visitors’ clubhouse at American Family Field, Alonso explained that he had picked a pumpkin this week ahead of a thrilling series with the Brewers.

“Nothing says fall more than playoff baseball and pumpkins,” said Alonso, who was collecting pumpkins with his wife, Haley, at a farm about 25 to 30 minutes outside of town.

Manager Carlos Mendoza, who won his first playoff series as a major league manager, also gave a rousing speech amid the chaos.

“We keep having fun, we keep smiling, that’s who we are here!” Mendoza said. “And we continue to believe: Let’s go!”

The skipper then joined in the fun by spraying champagne in the jubilant scene.