KANSAS CITY, Mo. — Pete Alonso wasn’t even sure he was going to make the New York Mets’ opening day roster, so even he never could have imagined the incredible season he’s having.

The burly first baseman hit his 40th home run to break the National League rookie record, capping a late outburst by the New York Mets in their 11-5 victory over the Kansas City Royals on Sunday.

“This season’s been unbelievable,” Alonso said. “It’s been a dream come true so far and I just want to keep building off of it and keep trying to help this team win.”

Michael Conforto hit a long homer in the first inning and drove in four runs. Amed Rosario put the Mets ahead 6-4 with a two-run single in the seventh, and Alonso went deep in the ninth.

Alonso quickly fell behind 0-2 in the count, but when Royals pitcher Jacob Barnes threw a high fastball, he didn’t miss.

“I was just trying to hit the ball hard like I have been,” Alonso said. “Take good, quality swings at good pitches and, thankfully, he gave me a fastball up in the zone, which I like to swing at.”

The result was a no-doubt shot over the bullpen in left field that snapped a tie with Cody Bellinger, who hit 39 home runs for the Los Angeles Dodgers in 2017 on the way to winning Rookie of the Year honors.

“It was a pretty grand one,” New York manager Mickey Callaway said. “It went a long way, it seemed like.”

Next up for the 24-year-old Alonso is the Mets season record of 41 home runs set by Todd Hundley in 1996 and equaled by Carlos Beltran a decade later.

“That’s even more mind-boggling,” Alonso said. “I’m just really grateful. Grateful and thankful and happy that I’ve had this opportunity.”

New York, in the middle of a crowded NL wild-card race thanks to its second-half surge, completed a 3-3 road trip and improved to 24-10 since the All-Star break.

Alonso also had an RBI double and scored three times during his second consecutive three-hit game. Rosario had three hits and three RBIs in the leadoff spot, and Joe Panik added three hits as the top four batters in the Mets’ lineup combined to go 11 for 18 with nine RBIs and seven runs.

“When we’re locked in and try to put good at-bats together and hit the ball hard and not try to do too much, I mean, we can be really dangerous,” Alonso said. “Today we showed that.”