CLEVELAND — If Josh Hart had any jitters Saturday over playing in his first playoff game, he did a great job of hiding them.

He looked like a poised postseason veteran, someone accustomed to coming up big in such moments. The Knicks’ key trade-deadline acquisition was instrumental in their thrilling 101-97, Game 1 victory over the favored Cavaliers at Rocket Mortgage FieldHouse.

“Oh man, that was fun. It was a great atmosphere,” Hart said. “Gotta give their fans credit. They showed out, they were loud, always supportive of their team. And obviously coming out with a win, that’s always gritty.”

Hart was all over the floor, scoring 17 points (seven in the fourth quarter), adding 10 rebounds and sinking the game’s biggest shot, a go-ahead 3-pointer with 1:49 left that gave the Knicks the lead for good.

He had to wait six seasons to finally reach the playoffs, and he made the most of his debut.

“Unreal, that’s what he does,” Jalen Brunson said. “I said it after the game: It doesn’t matter if it’s pickup, preseason, playoffs, he plays that way every single time. That’s just how he is, that’s how he’s wired. He’s big time.”

In 33 impactful minutes, Hart did a little bit of everything.

He spent large portions of the game defending Cavaliers star Donovan Mitchell.

He was a terror on the offensive glass, giving the Knicks extra possessions with five of their 17 offensive rebounds.

He scored in transition and even hit that big 3-pointer.

It was everything the Knicks have seen out of Hart since team president Leon Rise acquired him from the Trail Blazers the day before the trade deadline in exchange for Cam Reddish and a lottery-protected first-round pick.

It wasn’t a splashy trade, but it was a valuable one.

The Knicks won their first nine games with Hart. Saturday, they picked up their first road playoff win in a decade.

Without Hart, that wouldn’t have been possible.

“He’s a playmaker,” Thibodeau said of Hart, who went 8-for-11 from the field. “He’s gonna make hustle plays, make tough plays. He’s a great competitor. And he just plays to win. There’s no agenda other than winning with him.”

His biggest moment was the 3-pointer with under two minutes to go. The Knicks had fallen behind for the first time since early in the opening quarter after the Cavaliers had reeled off nine straight points. The Knicks were scrambling for a shot, with Cleveland successfully keeping the ball out of Brunson’s hands. Hart wasn’t afraid of the moment.

“Donovan did a good job of denying him, and it was like, ‘All right, gotta be aggressive,’ ” Hart said. “Pulled up and the ball went in.”