There is a lot more working for Pete Alonso than pure polar bear strength.

His balanced swing has catapulted him to the major league home run lead with 45 as the Mets host the Phillies on Friday night at Citi Field for the first of three games.

Growing up, Alonso said he studied taekwondo, the art of unarmed self-defense characterized by the extensive use of kicks, and he believes that has helped him become the gifted ballplayer he has developed into in his amazing rookie season.

It really helps with plays at first base where he has shown the ability to hang onto the bag on wide throws just long enough to record the out, saving infielders from throwing errors. Alonso has one of the longest stretches in the game and catches throws far out in front of the bag.

The 6-foot-3, 245-pounder has mastered the split at first base to get runners out by the slimmest of margins.

When asked about his ability to snare throws, contorting his body at different angles, Alonso revealed the deeper skill set.

“When I was younger I used to take taekwondo,’’ Alonso told The Post. “If baseball didn’t get in the way, I probably would have been a really advanced black belt. I was really good.’’

Alonso then said: “If I told you I can do a 180 split, would you believe me?’’

After what Alonso has done in the first 139 games of the Mets season, I almost believe polar bears can fly.

So do Mets fans.

Alonso, 24, has saved the Mets. His fifth-inning home run in the Mets’ 8-4 win over the Nationals on Wednesday at Nationals Park extended his current on-base streak to 30 games — the longest active streak in the majors. During that span, Alonso is hitting .308 with six doubles, 11 home runs, 28 RBIs, five hit by pitches and 20 runs scored. He has blasted seven home runs against the Nationals this season. No other player has more than five.

Then there have been all those plays at first base.

“He’s the best I’ve ever seen at stretching at first base,’’ Mickey Callaway told The Post. “He catches balls where he is laying down. It’s unbelievable. We talk about it all the time on the bench when he does it. He can be laying down picking balls, amazing.’’

These are the five tenets of taekwondo: courtesy, integrity, perseverance, self-control and indomitable spirit.

That pretty much sums up the scouting report for Alonso, who came into the majors with a reputation of being a poor defender but has proven to be one of the best first basemen in terms of receiving throws and making those stretches where he balances himself on the edge of the base.

He credits his early taekwondo training for that ability.

“That’s been a big part,’’ Alonso said. “Just staying flexible and as balanced as possible.’’

In spring training, Alonso told The Post about his book on baseball that he keeps in his locker, a simple middle school composite notebook where he records his thoughts and scouting reports.

He does whatever he can do to give himself an edge and remains positive about the team, saying of the Mets’ uphill battle for the second wild-card spot, “We’re extremely together. We battle and we have each other’s back and I think that’s been the key for us all year. We’ve come so far and we are just going to keep pushing forward. Keep pushing each other.’’

Callaway knows better than anyone what Alonso brings to the table every game.

“He poses a threat every single at-bat,’’ Callaway said. “With him in your lineup, even if he doesn’t get a hit, he may be the reason you score eight runs.’’

For the season Alonso is hitting .267 and has a .960 OPS. He has already set the Mets single-season home run record and is the first Met with a 100-RBI season since David Wright in 2010. He could top Aaron Judge’s rookie record of 52 home runs and is the first rookie to set his club’s franchise record for home runs since Pittsburgh’s Johnny Rizzo in 1938 with 23.

The Mets are lucky baseball did get in the way of taekwondo as Alonso has become a black belt in his sport of choice.

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