Juan Soto, who inked a record $765 million, 15-year deal to join the New York Mets in December, made an instant impact in his first spring training game with his new team, belting a 426-foot home run in his first at-bat.

Soto, who jumped to the success-starved Mets from the glamorous crosstown rival Yankees after helping the Bronx Bombers reach last year’s World Series, staked the Mets to a 1-0 lead over the Houston Astros in the first inning of their eventual 6-2 win in Florida.

“It was pretty incredible, I’m not going to lie,” said Mets manager Carlos Mendoza, who placed Soto second in the lineup between Francisco Lindor and Pete Alonso.

“Been watching this guy take some live at-bats for the past four or five days and then just having the ability to turn the switch like that — you put a different guy on the mound with a different uniform and he’s just locked in,” Mendoza said after seeing Soto drill a 2-1 pitch from left-handed hurler Colton Gordon to left center field.

It’s just what the Mets were hoping for when they landed the offseason’s marquee free agent, with Soto saying when he arrived in December that he wanted to be part of bringing the Mets their first title since 1986.

“He was just a different guy in the box today,” Mendoza said. “Whether he was taking pitches, when he swung through that fastball, you just saw his demeanor in the box.”

Soto drove in another run in the second inning and said he was pleased to get his Mets tenure off to a solid start.

“It’s been really cool to see (fans) enjoying the moment and enjoying this time,” the 26-year-old Dominican said. “First year with the Mets and everything, it’s going to be unforgettable.”