Mets first baseman Pete Alonso is congratulated by teammates in the...

Mets first baseman Pete Alonso is congratulated by teammates in the dugout after scoring during the seventh inning of a game against the Royals at Kauffman Stadium in Kansas City, Mo., on Sunday. Credit: Getty Images / Jamie Squire

KANSAS CITY, Mo. — In the waning minutes of an ordinary win on a slow Sunday afternoon, Pete Alonso made more history.

His solo home run in the ninth inning of the Mets’ 11-5 win over the Royals was his 40th of the season. That is more than any other rookie has hit in the 144-year history of the National League, one better than Dodgers star Cody Bellinger’s total in 2017.

The record-breaking shot soared over the visitors’ bullpen and a small section of seats in leftfield, traveling an estimated 418 feet after coming off the bat at 111 mph. Alonso got the ball back from a family of Royals fans, and after he gifted them a signed bat, a pair of cleats and a few autographed baseballs, the new keepsake rested in his locker, next to No. 39 from Atlanta on Thursday.

“Coming into camp, I didn’t know if I was going to make the team,” said Alonso, who arrived at spring training in a first-base competition with Dominic Smith, Todd Frazier and J.D. Davis. “To break this record and have a good season and keep playing the way I’ve been playing, just trying to help this team win, this season has been unbelievable.”

Alonso has a shot at the major-league rookie homer record, 52, set by the Yankees’ Aaron Judge in 2017. But up next is the Mets’ single-season high — rookie or otherwise — of 41. Todd Hundley (1996) and Carlos Beltran (2006) share that mark.

“It’s even more mind-boggling,” said Alonso, who also had an RBI double in the Mets’ six-run seventh.

Said Mickey Callaway, “If you would’ve said that three years ago or probably two years or even when we saw him last spring training [2018], people would’ve looked at you like you had two heads. That’s a lot of hard work and dedication. You have to be so proud for a kid like that.”

The blast from Alonso (3-for-4), whose two RBIs gave him 95, highlighted the win for the Mets (64-60), who outhit the Royals 16-6 and took the series after dropping the opener Friday. The Mets, who are two games out of a wild-card spot, finished their road trip to Atlanta and Kansas City at 3-3.

The game turned in the seventh, when the Mets erased a 4-3 deficit by scoring six runs after Kansas City decided to go to its bullpen instead of sticking with righthander Glenn Sparkman (81 pitches).

Davis had a tying pinch-hit single and Amed Rosario (3-for-5) added a two-run single before the Mets poured it on. Richard Lovelady in particular got pounded, facing four batters and allowing four hits.

Sparkman largely stifled the Mets, giving up three runs in six innings. All of the runs came on one pitch: Michael Conforto’s three-run home run to rightfield in the first inning. The 452-foot shot was Conforto’s 26th homer of the year, two shy of the career high he set last year.

That concluded a humdrum weekend for the Mets against KC starters. Mike Montgomery (4.63 ERA) held the Mets to an unearned run in six innings Friday. Jakob Junis (4.78 ERA) also turned in a quality start, allowing three runs in 6 1⁄3 innings Saturday. Then Sparkman (5.40) made the one mistake to Conforto.

“We got to the starter in the first and he really silenced us pretty good for the rest of his outing,” Callaway said. “They brought in the bullpen and we grinded every at-bat out. We went the other way when we needed to, we got the bunt down when we needed to. We did the small things, and those tend to pay off.”

Zack Wheeler turned in his second mediocre start of the week, allowing four runs (three earned) in five innings. He didn’t allow a hit through the first three innings, but he petered out late and committed a key throwing error during Kansas City’s three-run fifth.

After a day off Monday, the Mets will begin a difficult homestand against three teams holding playoff spots: the Indians, Braves and Cubs.

“We know what time of the season it is. It’s time to go,” Alonso said. “Not every game is do-or-die at this point, but every game matters a lot. We all recognize that.”

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