Citi Field has been reinvigorated.

As the Mets trailed 3-1 in the National League Championhip Series to the Dodgers on Friday night in New York, fans held a newfound energy — one that Francisco Alvarez helped feed.

The 22-year-old Mets catcher broke out of an abysmal postseason slump to go 3-for-4 with an RBI and a run scored in a 12-6 victory. Alvarez has now reached base in five of his last six at bats, and has four hits in the last two games.

Mets manager Carlos Mendoza said earlier in the week that Alvarez was having trouble making good swing decisions at the plate because he was late on the fastball, something that he appears to have corrected over his last several at-bats.

“I was ready for a fastball,” Alvarez said after the game. “I reacted early which is what I’ve been working on, being shorter to the ball so that react to the fastball quicker and it doesn’t beat you. I’m seeing the ball better and feel better at the plate as a result of that.

Two days ago, fans were calling for Alvarez to be benched. But in Friday’s must-win game, he proved himself worthy of a spot in this playoff lineup.

“I think the biggest thing was trying to keep it simple,” Mendoza said. “Not trying to swing too hard, and just be short to the ball, be on time, basically just relax. When you’re struggling, there’s a lot of people in your ears, ‘You need to do this, you need to do that.’ Especially at this time of year, the simpler the better. And that’s what he did.”

Alvarez breaking out of his slump added much-needed juice to an offense that has been stagnant overall in the last two games. In Games 3 and 4, the Mets stranded 33 runners on base and were 4-for-27 with runners in scoring position.

In Game 5, they did not strike out once.

Mendoza had defended his decision to stick with Alvarez in the lineup, saying, “He’ll come through for us.” It took until the 12th game of the playoffs for that to happen, but it was the most important one yet (as each successive game keeps becoming).

Flaherty flops: Instead of pitching his hometown team into the World Series, Jack Flaherty sent the NLCS back to Los Angeles.

Dominant in the opener, Dodgers starter Flaherty flopped in Game 5.

Pete Alonso hit a three-run homer in the first and the Mets beat up Flaherty for five runs in the third inning of the 12-6 victory.

“He wasn’t sharp, clearly,” Dodgers manager Dave Roberts said of the 29-year-old right-hander. “He’s been fighting something. He’s been under the weather a little bit. So I don’t know if that bled into the stuff, the velocity. I’m not sure.”

A high school teammate of Max Fried and Lucas Giolito at Harvard-Westlake in Los Angeles, Flaherty was dealt to the Dodgers by the Tigers on July 30. He went 6-2 with a 3.58 ERA for the NL West champs.

In the ALCS between the Yankees and Guardians, Game 5 on Saturday night in Cleveland ended too late for this edition.

The Yankees had led 3-1 in the series after Friday’s 8-6 victory.