NEW YORK — Yep, it happened again.
The Celtics have spent this season blowing leads, botching fourth quarters, and losing close games, and Thursday they saved perhaps their most-telling performance for Broadway.
Racing to a 25-point lead only to again lose that margin late, the Celtics needed one stop to force overtime. But this team appears cursed as RJ Barrett caught the inbounds pass and fired a 3-pointer that banked in to hand the Celtics an excruciating 108-105 loss.
The Celtics led by 20 midway through the third quarter but as has been their pattern, their offense became stagnant and the Knicks caught fire offensively, especially former Celtic Evan Fournier, who scored a career-high 41 points on 10 of 14 from the 3-point line.
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Jayson Tatum tied the game with a fadeaway jumper with 1.5 seconds left, just enough time for another heartbreak.
Barrett caught the ball, surrounded by defenders and just fired it at the basket. Bucket.
It’s the sixth time in 16 days the Celtics have lost a game they were either tied or led in the fourth quarter. Coach Ime Udoka said he believes the issue is becoming mental.
“I think it’s the lack of mental toughness to fight through those adverse times,” he said. “Across the board, it’s a turnover here, a bad shot here, missed defensive assignment here, several missed rebounds tonight. It’s a lot of different things.
“Like I said, a calming presence to slow it down and get us what we want is really what you need at that point.”
“I feel like [Udoka] is 100 percent right, to be honest,” said center Robert Williams. “We get rattled a lot. We’ve just got to find it within ourselves to grit and to fight and to just come together even when stuff is not going our way. Like coach said, it’s obvious we get rattled when we face adversity.”
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Tatum was stellar with 36 points, 6 rebounds, 9 assists and 2 steals. But he was the lone Celtic to respond offensively in the final quarter, scoring 13 of Boston’s 21 points. Jaylen Brown scored 12 points in the first 6:22 but did not score in the fourth quarter.
“This stretch is tough, losing leads and just not finishing out in the fourth quarter,” Tatum said. “I think we have to harp on and keep reiterating that whatever was working when we were getting the lead in the first half, not shy away from it. Don’t get bored with the details.”
Udoka used Marcus Smart and Dennis Schröder together down the stretch but opted for Tatum to be the primary ball handler. It resulted in open 3-pointers for Smart, but he missed three open looks in the final 5:29. Tatum scored every Celtics basket in the final 7:22.
“Marcus missed a few at the end but across the board we aren’t having the best shooting year,” Udoka said. “Regardless of who we have handling (the ball) out there, it’s not always going to be the best shooters on the court, especially when you have some defensive lineups as well.”
Udoka pointed out that only Grant Williams and Josh Richardson were having better-than-average shooting seasons. Neither played in the fourth quarter.
The Celtics were 6-for-17 shooting in the fourth quarter, with Tatum scoring 13 of their 21 points. Julius Randle scored 22 for the Knicks and Immanuel Quickley added 16 off the bench. The Celtics were 6 of 22 from the 3-point line in the second half.
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The Knicks were the aggressors in the third quarter, making two runs at the Celtics. Barrett and Fournier began the period with consecutive 3-pointers and the Celtics’ lead was down to 10.
Boston responded behind Tatum with an 18-8 run to extend the lead to 81-61, and the Madison Square Garden fans pelted the home team with boos after a 24-second clock violation.
That reaction appeared to change the game.
The Knicks used Quickley and Randle to end the quarter on a 16-3 run to cut the Boston lead to 7, and the Celtics had lost all of their confidence. Shots were missed, turnovers made and defensive mistakes increased.
The first 10 minutes of the second period was a best-case scenario for Udoka. The Celtics were stifling on defense, holding the trio of Barrett, Randle and Alec Burks to 1-for-16 shooting at one point while the 3-balls were falling for the offense.
Boston began the period on 13-for-18 shooting and 8 of 11 from the 3-point line as Tatum and Schröder got hot, combining for five 3-pointers. The Celtics raced to a 57-32 lead after a Schröder 3-pointer with 3:53 left in the second quarter.
The Knicks responded with a 15-6 run to end the half, cutting the Celtics’ lead to 16 and seizing the momentum. New York scored 8 points in the final 1:05 after a series of missed Celtics shots and turnovers.
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The Celtics were 15-for-23 shooting in the second period overall with Tatum scoring 15 of their 38 points. The Celtics led, 63-47, at halftime and it was a positive response after Wednesday’s loss.
Yet, with their history of blowing leads, the Celtics knew it would take just as productive of a second half to earn the victory.
The Celtics were coming off one of their most disappointing losses of the season, a 99-97 setback to the San Antonio Spurs as Brown missed a potential tying layup at the buzzer. Yet, they were brimming with energy at the outset Thursday, jumping out to a 19-6 lead behind 12 points from Brown.
Gary Washburn is a Globe columnist. He can be reached at gary.washburn@globe.com. Follow him on Twitter @GwashburnGlobe.