NEW YORK — The Celtics bid for back-to-back NBA titles officially is on life support after yet another second-half nosedive.
Looking to even the Eastern Conference semifinals at two games apiece, the defending champions instead squandered a 14-point third-quarter lead and a standout performance from Jayson Tatum in a 121-113 loss to the New York Knicks on Monday night at Madison Square Garden.
Boston now must win the next three games — beginning with Game 5 on Wednesday at TD Garden — to extend its season. And it might need to do so without its best player.
After racking up 42 points, eight rebounds, four assists, four steals and two blocks, Tatum suffered an ankle injury midway through the fourth quarter and had to be helped off the court by Celtics staffers.
Jalen Brunson spearheaded by far the Knicks’ best offensive outing of the series, going off for 38 points and 12 assists. Fellow New York starters Karl-Anthony Towns, Mikal Bridges and OG Anunuoby all topped 20 points, as well, with Bridges delivering several clutch makes to help the third-seeded Knicks pull away late.
In NBA history, teams that fall behind 1-3 in a playoff series go on to lose 95.6% of the time. No team has successfully completed a 1-3 comeback since 2020.
Boston blew third-quarter leads of 20, 20 and 14 points in its three losses to New York, which now sits just one win away from its first Eastern Conference finals appearance since 2000.
The Celtics got off to another excellent start, building a double-digit first-quarter lead for the third time in this series. Derrick White (23 points) made his first four 3-pointers, and Tatum foiled two early Knicks possessions with a block and a steal. The latter led to a fast-break layup that triggered a Tom Thibodeau timeout.
New York briefly stabilized after that stoppage. It took the hosts just over three minutes to erase Boston’s cushion, with Anunoby hitting a corner three to cap a 13-3 Knicks run. But the Celtics responded with a 14-2 run fueled by more red-hot perimeter shooting.
Boston scored on its final seven possessions of the first quarter, including three Tatum 3-pointers (two over Towns, one over Brunson). The Celtics shot 9-for-14 from deep in the opening frame and led 39-28.
Disparities in the margins prevented the Celtics from extending that lead, as the Knicks doubled them up in offensive rebounds (8-4), second-chance points (11-4) and points in the paint (24-11) in the first half to remain competitive. Boston was able to weather New York’s multiple second-quarter pushes, however, staging a 12-3 run after a driving layup by Towns made it a four-point game.
Tatum ignited that surge with a 3-pointer — part of a 20-point first half for the Celtics star — and Porzingis helped maintain it with two offensive rebounds, a putback tip-in and a steal under Boston’s basket. The Celtics big man upped his activity Monday night, playing 24 minutes after going sub-20 in the first three games, but his effectiveness waned as the night progressed and he appeared to tire.
The Celtics also kept Brunson and the rest of his Knicks teammates off the foul line until the final two minutes of the first half, attempting 15 free throws before New York took its first. They took a 62-51 advantage into halftime.
Tatum sparked another big sequence early in the third quarter. In one 77-second span, he threaded a pass to Jrue Holiday for a layup, hit a three, intercepted an ill-advised Towns pass and found White in the corner for another triple that put Boston up 14.
But a costly error by Tatum’s co-star gave New York life. After Brunson made a three and a layup on consecutive trips, Jaylen Brown was whistled for a flagrant foul when he placed his foot into the Knicks point guard’s landing zone on a 3-point attempt. The Knicks were awarded three shots and the ball, resulting in a four-point possession that cut the Celtics’ lead to five.
Even after Boston responded with a White three and a steal-and-score by Tatum, the Knicks kept charging. They steadily chipped away until Brunson’s midrange jumper over White tied the game at 83-83 with 1:07 left in the third. Anunoby and Josh Hart then closed the quarter with a made three and a fast-break layup to cap a 30-13 run for New York, which led 88-85 heading into the fourth.
Brunson poured in 18 points in the third quarter. While he heated up, Boston’s offense stagnated, lacking the ball movement and flow that served them well earlier in the night. Tatum missed his final four field-goal attempts of the third — all pull-up threes — a landed hard on his injured right wrist on a drive to the basket.
Both teams entered precarious foul-trouble situations early in the fourth quarter, with Hart and Brown both picking up their fifth and Towns committing No. 4. With Brown on the cusp of disqualification, the Celtics opted to roll with a double-big lineup featuring a visibly fatigued Porzingis, who looked a step slow on both ends.
Tatum did his best to power the Celtics with two threes and an and-one layup.