NEW YORK — The Mets are still in the National League Wild Card race, and the next 11 days could determine if they play October baseball as they face contenders in the Orioles, Padres and D-backs. But for one August night, with one swing of the bat, Francisco Alvarez brought a playoff atmosphere to Citi Field.

Facing Baltimore closer Seranthony Domínguez in the ninth inning, Alvarez received the green light from manager Carlos Mendoza to swing 3-0 and he did not miss, launching a walk-off homer to give the Mets a 4-3 victory.

It was a no-doubter off the bat, with an exit velocity of 106.5 mph and a projected distance of 421 feet, and Alvarez let the emotions come pouring out of him almost as soon as he made contact. The fiery 22-year-old catcher dropped his bat, took two steps out of the box and pointed emphatically downwards before beating his hand against his chest, letting everyone in the stadium know whose house they were in. The Citi Field crowd responded in kind.

“It was good to see him get ready, be on time,” Mendoza said. “You know you are going to get a plus fastball from Domínguez, who is throwing 98, 99, up to 100. Alvy stayed short, getting the head out, and finally … Good for Alvy to get that feeling back, and he won out. It was huge for us.”

Alvarez took his raucous trip around the bases after the first walk-off hit of his career and was mobbed by his teammates at home plate. So mobbed, in fact, that he might have missed touching home in all the excitement.

“I don’t know if I missed [home plate], but I came back to touch it,” Alvarez said.

It was the third walk-off homer on a 3-0 pitch since 2020. The last to do it was Tigers infielder Nick Maton against the Giants on April 14, 2023.

“I was thinking, swing the bat and hit the barrel,” Alvarez said. “I knew it was [gone]. I put the bat on the ball. … I feel very excited, because the Orioles are a pretty good team. We beat them.”

When Alvarez was in the batter’s box, Mendoza was talking to pitching coach Jeremy Hefner about a bullpen move if the game went extra innings and then, suddenly, the game was over.

Never mind.

“I looked around and the ball was already in the air,” Mendoza said. “The feeling was incredible. Guys were jumping around. Overall, I thought it was a good win for us.”

It was a hit Alvarez needed. Entering Monday’s action, Alvarez was 12-for-72 since the All-Star break. He was chasing a lot of pitches, but he has been trying to perfect his swing by taking early hitting practice.

“It has been hard for him,” Mendoza said. “He is 22 years old and struggling at the big league level. I’ve been saying it: He cares so much, and he wants us to win. At times, when we are struggling offensively as a team, he feels like he is responsible, and he has a lot on his plate with taking care of the pitching staff and things like that. … But to finally hit one out of the ballpark, it has been a while. In that situation to give us a win, I’m happy for him.”

Alvarez was behind the plate when left-hander David Peterson threw his best game of the season, lasting a season-high seven innings and allowing three runs — two earned — on six hits. It was going so well for Peterson until the seventh inning, when he balked in a run and then allowed a game-tying home run to Ramón Urías.

“I felt like Alvy and I had a good plan, and we were able to execute. We were able to go right after them,” Peterson said.

But the game was highlighted by Alvarez, a guy who is known to come through in the clutch.

“It was a roller coaster of a game, but Alvy lives for those moments, and he is a really special kind of player,” Brandon Nimmo said. “I know things haven’t been going as he would like, but that doesn’t mean anything to him in those situations. He just needs that one time, and he always looks for it. I’m so happy for him. It couldn’t have happened to a better guy.”