Celtics guard Payton Pritchard steals the ball from Knicks forward Julius...

Celtics guard Payton Pritchard steals the ball from Knicks forward Julius Randle during the first half of an NBA game on Monday in Boston. Credit: AP/Charles Krupa

BOSTON — You will never get Tom Thibodeau to admit that his team is shorthanded or to using an absence as a crutch. But facing the Boston Celtics, on the road, in the second night of a back-to-back set, without the player who has been their most consistent force is a task that someone can say for him — is too much to overcome.

The Knicks were without RJ Barrett, arguably their best player through the early stage of the season, as he was sidelined with a migraine. And the Knicks fought for much of the night, hanging around until early in the fourth quarter when the Celtics just began to assert their dominance, pulling away for a 114-98 win at TD Garden.

The loss snapped a three-game winning streak for the Knicks.

Maybe the Knicks would have seen a similar result under different circumstances, rested and armed with a full lineup. The Celtics are the team that has been considered the favorite to reach the NBA Finals out of the Eastern Conference and looked every bit of it as they took over the game in the fourth quarter.

Barrett entered the night as the Knicks leading scorer this season at 22.6 points per game and has been connecting on 50% from beyond the arc.

Without him, the Knicks are now 0-3 on the season. With Barrett out, Josh Hart got the starting assignment and Thibodeau trimmed his rotation down to just eight players until the final minute when he pulled the plug and went deep into his bench.

Jalen Brunson led the Knicks with 26 points and Julius Randle added 25. Hart chipped in 16 and nine rebounds in 43 minutes, but it wasn’t nearly enough. Jayson Tatum led all scorers with 35 points — 17 coming in the fourth quarter, Jaylen Brown added 22 and Kristaps Porzingis was a problem matchup all night with 21 points.

“I mean, he’s a great player, he’s a great scorer,” Randle said of Tatum. “The game always balances out or evens out. Josh, the other guys, did a good job of making it tough for him. Unfortunately he got it rolling there in the end. He hit some deep threes there, too.”

The Knicks did try to share the responsibility but no one could stop Tatum in the fourth quarter, a task that has confounded most teams in the NBA.

The Knicks closed a double-digit deficit to three early in the fourth quarter with Hart first delivering — losing the ball as he rose for a jump shot, but bouncing it off Jrue Holiday’s back, catching it and draining a three. Brunson then buried a three and the Knicks were down 91-88. But on the other end, Tatum, who was 1-for-8 from three to this point, converted a three, drawing a foul on Hart on the play for a four-point play and a 95-88 Boston lead. When Holiday buried a three with 7:01 left the Celtics were back up by 10 and the Knicks were heading to a timeout.

Even shorthanded the Knicks managed a 53-52 halftime lead, but not one they felt great about heading to the locker room. The Knicks were up, 51-43, after a Quentin Grimes three-pointer with 1:33 left in the second quarter, but a 12-5 finish for the Celtics cut the lead to one and the way it happened was the sort of sequence that causes Thibodeau’s blood to boil.

After a Porzingis bucket, Brunson had a drive blocked by Derrick White and Tatum leaked out ahead of the pack for a breakaway dunk. Randle then misfired on a forced three-pointer and his defender, Payton Pritchard, slipped through for an uncontested layup. Brunson hit a tough jumper, but the defense faltered again, giving up a three-point field goal to Jaylen Brown at the buzzer.

“Just closing out the quarters,” Thibodeau said. “We didn’t close out any quarters as well as we should have or could have. So that was probably the biggest thing. We were up eight with [1:30] to go. Same thing happened in the first and end of the third. I thought we played pretty well the first half. We didn’t protect our basket right at the end of that last minute and a half. Against them a bad minute can be 10 points and it was.”

The Knicks saw the end of the third quarter bring trouble, too as the Celtics stretched the lead to 10 with 10.6 seconds left when Brown stole the ball from Randle and when Randle was slow getting back into the play, Jrue Holiday sunk a wide-open three. A pair of free throws by Immanuel Quickley with 1.6 seconds left cut the deficit to 84-76 entering the final period.

“That was important,” Porzingis said. “We knew they were that kind of team that could finish the quarters and create momentum for them. But actually, we did that. Before the halftime, we created the momentum for ourselves and then we came out in third or fourth on a different level.”

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