CINCINNATI — Pete Alonso’s power is crazy. How crazy?

Alonso crushed his 50th home run of the season Friday night, an epic 437-foot, eighth-inning rocket to the Riverboat Power Stacks in right-center at Great American Ball Park in the Mets’ 8-1 win over the Reds.

That blast backed another Jacob deGrom work of art as Alonso became only the 30th player in major league history to join the 50-home run club and the first Met to do so.

That’s it, 30 players.

Alonso became only the second rookie to hit the 50-homer mark, joining Aaron Judge who hit 52 in 2017. And he reached 50 career homers faster than any other player in MLB history (152 games).

“That’s crazy,’’ Alonso told The Post about joining such historic ranks, especially the 50-homer club. “That’s absurd, 19,000 people to ever play the game of baseball, that’s ridiculous.’’

The Mets will need him to keep producing to keep their slim postseason hopes alive.

Look at some of the names on the 50-homer list: Babe Ruth, Willie Mays, Barry Bonds, Mickey Mantle, Ken Griffey Jr., Roger Maris, Jimmie Foxx and George Foster of the Big Red Machine.

Since 2000, 13 players have hit 50 home runs in a season led by Bonds’ 73 in 2001. Other names include Alex Rodriguez, David Ortiz, Judge, Jim Thome, Giancarlo Stanton and Sammy Sosa.

The Manfred Ball flies, but Alonso has made it really fly. Mickey Callaway said Alonso’s homer went at least 100 feet farther than it was marked at 437. Alonso leads the NL with those 50 home runs, two ahead of the Reds’ Eugenio Suarez.

That was the game within the game Friday night. And deGrom, of course, is gunning for his second straight Cy Young award.

Alonso has made all this happen by being an incredible student of the game in addition to having incredible power. He keeps daily notes of his at-bats, the good and bad, to make himself the best hitter he can be on a game-by-game basis.

“It’s crazy with guys like Babe Ruth, Barry Bonds, Sammy Sosa, Mickey Mantle, Willie Mays, it’s ridiculous to kind of wrap my mind around that,’’ Alonso told me of joining such a prestigious home-run club.

Alonso owns 115 RBIs, the third most by an NL rookie, with only Albert Pujols (130 in 2001) and Wally Berger (119 in 1930) driving in more runs.

What has enabled Alonso to make the needed adjustments throughout a rookie season during which he has homered in 16 different ballparks — the most parks in which a rookie has homered in one season — and posted a .302/.383/.615 slash line on the road with 26 home runs.

“Just constant work,’’ Alonso said. “It’s an evolving game. You can’t just be a dinosaur.’’

Or just a polar bear.

“You have to learn how they are getting you out and you have to adjust, you have to adapt to whatever they are doing and form your own plan of attack,’’ Alonso said. “I’ve been simplifying everything. If I’m thinking too much or I’m too fine or if I’m trying to do too much, that usually doesn’t work.’’

He uses his notebook in a critical fashion.

“There is a lot of information in there,’’ he said. “I like to have that to kind of see my thoughts on days I do well and also on the bad days too so I can steer away from trouble. I just give an honest assessment.’’

Alonso is a student of hitting and a student of life. Every day is a learning opportunity and the Mets are lucky to have him leading the way.

“He’s a leader in every sense of the word,’’ Callaway said.

As for the home-run race, Alonso said: “That’s cool, but for us, it’s playing for a playoff spot. That’s what it’s about.’’

Alonso’s family has Ohio roots and his father was at the game.

“My dad grew up watching the Big Red Machine,’’ Alonso said. “Johnny Bench, Pete Rose, Joe Morgan, that’s one of the best teams in baseball history.’’

Now his name will be up there with the greatest home-run hitters of all time. Crazy.