Celtics coach Joe Mazzulla was immediately impressed by Brissett’s play, especially considering that Mazzulla didn’t play him in the regular-season opener against the Knicks.

“He didn’t play in Game 1, and he changed the game,” Mazzulla told reporters. “That, to me, is what momentum is all about. He came in, he made a significant impact, and he did his job at a high, high level.

“We have to get to a point where what he did is just as important as what the other guys have done tonight, and he helped us win.”

Celtics star Jayson Tatum was on the bench for much of Brissett’s first stretch on the floor, but he also sensed the impact that Brissett had on Friday’s game.

“He was the sole reason that we got back into the game, and I told him that,” Tatum said. “He came right in, and we were kind of flat. His energy, his offensive rebounding, him giving us second- and third-chance opportunities was big. And that’s his job.

“For him to come to do that — not playing the last game, to come in today and give us this spark to turn the game around was huge. And that’s what I love about our team.”

Brissett was viewed as a potential successor to Grant Williams’s spot in the rotation when he signed with the Celtics over the offseason, agreeing to a deal with Boston in the opening hours of free agency as Williams departed for Dallas shortly after. He didn’t play on Wednesday as Mazzulla opted to make center Luke Kornet the ninth man in the rotation against the Knicks, playing three bigs.

Mazzulla wanted to get Brissett into the rotation for Friday’s game, but he planned on putting him on the floor later than he actually did. He changed his mind, though, for one reason.

“He was supposed to go in to start the second,” Joe Mazzulla said of Brissett. “But I felt like we needed him earlier and so you just kind of went with him and he did a great job.”

While Brissett wasn’t even a regular starter during his time with the Pacers over the last three seasons, he’ll certainly be adjusting and sacrificing with the Celtics. He was left out of the Pacers’ rotation just 17 times out of the 104 games he suited up for since December 2021, scoring 8.1 points per game as he averaged roughly 21 minutes per game during that stretch.

Brissett will almost certainly get more opportunities as the season wears on, but it’s clear that his role will be relatively limited when the Celtics are whole and healthy. He’s OK, though, with having to earn his spot in the rotation through hustle plays, recognizing the talent in Boston’s starting rotation.

“That’s who I am as a player,” Brissett told reporters of his performance on Friday. “Every night I’m going to try to do that no matter who we’re playing, no matter what night it is. But we’ve got real stars on this team. So me coming in, just being myself, not trying to do too much, not trying to prove that I can do anything else even though they all know I can.”