BOSTON — Tom Thibodeau described it best. Not much else really needed to be said.

Jalen Brunson had just eight points on rough 3-for-13 shooting from the field after three quarters. He looked set for by far his worst showing of the postseason.

The Knicks were floundering with their captain far from his best.

But when the game was on the line, the NBA’s Clutch Player of the Year showed up.

His pull-up jumper gave the Knicks their first lead of the game with 1:58 left. His layup — with his weak right hand — extended that lead to three with 56.5 seconds left.

After the Celtics regained the lead with Jayson Tatum’s dunk, Brunson did not hesitate.

He promptly did what he does best and drew a foul, then subsequently drilled both free throws to give the Knicks a 91-90 lead with 12.7 seconds left.

Mikal Bridges’ steal then secured a Game 2 91-90 win over the Celtics Wednesday night at TD Garden.

“That’s Jalen,” Thibodeau said. “It doesn’t matter what’s going on in the game, he’s going to be at his best when his best is needed.”

Brunson finished with 17 points on 6-for-19 shooting from the field along with seven assists.

His nine fourth-quarter points came after he poured in 11 during the fourth quarter of Game 1.

This postseason, he has a combined 86 points in the fourth quarter — 20 more than the next closest player, Anthony Edwards.

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And he’s done it while shooting 50.8 percent from the field and 41.2 percent from 3-point range.

He’s added 13 assists with just three turnovers as well.

“It’s a focus that I need to have in that element,” Brunson said. “Can’t really worry about what happened previously in the game. It’s all about focusing and having a clear mind, just trying to win the game. That’s just my mindset. I wouldn’t be able to without my teammates.”