Pete Alonso helps his New York Mets stay in the game… 

The 29-year-old half-Spanish American professional baseball player, nicknamed “Polar Bear,” hit an improbable home run on Friday to set the tone for the night.

The Mets first baseman hit a first-inning slider from the Los Angeles Dodgers’ Jack Flaherty at his feet to deep center field, a three-run, 432-foot blast that put the New York offense in gear in an eventual 12-6, season-saving win in Game 5 of the National League Championship Series.

The home run wasn’t a pitching mistake as much as it was a hitting marvel.

Alonso made contact on a pitch that was 1.12 feet above the ground, the second-lowest ball hit for a home run in the postseason in the pitch-tracking era (since 2008).

“I was just looking for something over the middle of the plate,” Alonso said when asked to explain how he got the barrel of the bat on Flaherty’s pitch. “I didn’t really realize how low the pitch was. I got caught a little out front. … Honestly, it’s inexplainable. It’s the magic of the postseason. And I’m just happy I squared it up.”

The home run sparked an incredible night for the Mets’ offense, one that did not include a strikeout by any New York hitter. It marked the first time a team hasn’t struck out in a postseason game since the Los Angeles Angels in the 2002 World Series against the San Francisco Giants.

“We didn’t strike out?” outfielder Jesse Winker said when informed of the accomplishment. “We didn’t strike out? Wow. I don’t think I’ve been part of a game like that. That’s amazing. We just have to keep doing that.”

The turnaround against Flaherty was striking. He shut out the Mets over seven innings in a Game 1 win but lasted only three innings in Game 5, giving up eight runs, eight hits and four walks.

“We didn’t chase his secondary pitches,” Mets manager Carlos Mendoza said. “We know he’s got that slider and the knuckle curve and he’s going to try to make us chase, and we didn’t do that today. And when he came in the zone with his fastball, we were ready, and that’s the key.”

After the game, Dodgers manager Dave Roberts revealed Flaherty wasn’t feeling his best.

“He wasn’t sharp, clearly,” Roberts said. “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.”

Flaherty averaged 91.4 mph on his fastball in Game 5, down from 92.6 in Game 1. His regular-season average was 93.3 mph.

After the loss, the veteran right-hander didn’t address how he felt during the game but offered this explanation for his issues: “I felt like for the first time in a while I let the game speed up on me a little bit and didn’t make the adjustments in-game.”

Roberts could have pulled him earlier, but knowing his team had a cushion in the series, he left him in while the Mets built a big lead.

As much as Flaherty struggled, credit has to go to the Mets, who had 14 hits, including four by Starling Marte and three by Francisco Alvarez.

“When it comes to hitting, at that point you just have to rely on capitalizing on the mistakes that the pitcher makes,” Marte said. “And thankfully that’s what I’ve been able to do in terms of getting the results.”

Though the Dodgers didn’t go quietly, the 43,841 fans at Citi Field saw the Mets respond every time.

The win sends the series back to Los Angeles for Game 6 on Sunday.

On paper, the Mets have the starting pitching edge as Sean Manaea will get the ball on five days’ rest; the Dodgers have planned a bullpen game.

“We’ve had our backs against the wall all season,” Mets designated hitter J.D. Martinez said. “Why should this be any different?”