BOSTON — While his teammates struggled around him, Karl-Anthony Towns kept the Knicks afloat.

And then in crunch time, he brought them within striking distance.

He finished with 21 points on 9-for-16 shooting from the field and grabbed 17 rebounds in the Knicks’ 91-90 Game 2 win over the Celtics Wednesday night at TD Garden.

“KAT, the way he started off the game was great for us,” Jalen Brunson said. “The way he’s been throughout the entire season, he’s been one of the best teammates we have. The way he gives us energy and the way he goes and gets rebounds and what he does, it doesn’t go unnoticed. It’s just the way he’s been.”

Towns scored 14 of his 21 points in the first half. Brunson finished the first half with just seven points, while OG Anunoby had five and Mikal Bridges was scoreless.

The Knicks entered the break down 50-41, but it would have been much worse if not for Towns carrying the scoring load.

With the Knicks trailing 86-82, Towns tipped in the rebound from Josh Hart’s missed layup, and was fouled by Al Horford on the play.

He made the free throw, cutting the Knicks deficit to 86-85 with 2:33 left in the game. Brunson took it from there.

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“The ball found me,” Towns said. “I was just trying to be aggressive and scoring and I got some good opportunities. To start the third [quarter], I saw how our energy was, I wanted to kind of bring a spark. I think being able to hit those early shots allows us to understand we’re in the game, and we started the third quarter better than we did last game.”

Towns had been quiet the previous two games — Game 6 against the Pistons in the first round and Game 1 of this series — with just 10 and 14 points, respectively. Wednesday represented much more of why the Knicks made the blockbuster trade to acquire him.

“Just seeing how the game was playing out, I wanted to make sure I did everything I could to put our team in a position to win,” Towns said. “In the first half, I was trying to do that. In the second half, didn’t want us to come out sluggish. I wanted to be a catalyst for energy.”