When it mattered most, Jalen Brunson strapped on his cape and exacted revenge on the Miami Heat.

Trailing by nine with under four minutes left — and by as many as 21 in the second half — the Knicks point guard, nursing a shoulder injury, nailed three clutch buckets for a 100-98 comeback on Black Friday, keeping the Knicks alive in the In-Season Tournament.

Brunson was nailed on his non-shooting shoulder by Bam Adebayo on an and-1 conversion with 2:56 remaining, wincing in pain on the court before recovering to attempt the free throw.

About 30 seconds later, Brunson drained a jumper to cut the deficit to 3, then another jumper with 1:24 left for a 3-point lead.

“I’m hurt,” Brunson said. “But I’m fine.”

The improbable Knicks victory finished with Jimmy Butler, the Knicks tormentor of the 2023 playoffs, missing a potential game-winning 3-pointer at the buzzer.

“It’s pretty cool,” Brunson said. “I’m not going to lie. It’s a really good win.”

“I was just praying [Butler’s shot] didn’t go in.”

Brunson finished with 24 points, including eight in the final three minutes despite facing a swarm of Heat defenders.

Just like in the playoffs — which finished about six months ago with the Knicks getting eliminated by the Heat — Miami coach Erik Spoelstra had no answer when the Knicks point guard found his groove.

“He’s a competitor,” Spoelstra said. “He’s going to try to impose his will on the game and that’s what he was able to do in that series. He was a handful. Even as prepared, it’s tough, our guys have been schooled on a lot of different pick and roll plays. He can kind of manipulate the floor in a different way. You have to respect that.”

Brunson said he heard a Knicks fan calling the team’s performance “embarrassing” before the comeback, which wasn’t necessarily motivating but definitely noted.

Soon the Garden exploded to its loudest decibels of the season.

“I say this all the time. It’s the best place in the world to play,” Tom Thibodeau said. “The best arena, best fans, best city. The atmosphere is terrific.”

Much of Friday followed a familiar script from the playoffs.

Butler was feasting with methodical play, recording 23 points on 7-of-14 shooting.

Adebayo neutralized Mitchell Robinson — who was plagued by foul trouble — dominating the paint while grabbing 11 boards. Julius Randle struggled with six turnovers and just 13 points on 5 of 12 shooting.

The Heat’s 19-0 run to start the third quarter looked like a backbreaker.

But everything changed in the fourth quarter. Miami (10-6) went ice cold while missing 18 of their 21 attempts in the final period, while the Knicks rode their bench for the start of the comeback before giving the ball to their point guard.

Immanuel Quickley finished with 20 points off the bench for the Knicks.

“They hit us pretty hard to start the third,” Thibodeau said. “But we hit them back.”

With their most impressive win of the season, the Knicks (9-6 in the regular season) are 2-1 in the group play of the In-Season Tournament and could advance to the quarterfinals with a victory Tuesday against the Hornets.

They beat their rivals and survived, while Butler vowed his next potential game winner won’t fail. The Knicks don’t play the Heat again until late January.

“I thought that [the last shot] was going in, I’m always looking for the win,” Butler said. “Myself, and everybody else is riding with me. We’re [the Heat] going to live with the result, but I guarantee I’m going to make the next one.”