BOSTON — When the game began there were the usual signs of life at TD Garden, the Dropkick Murphys echoing through the arena as the teams took the floor and the fans loudly booed the Knicks’ arrival.

But Jayson Tatum was in street clothes near the bench and much of the Boston roster that had won a title two seasons ago and dominated the Knicks in the regular season last year — and built a 20-point halftime lead in the first two games of the playoff meeting last season — was gone.

So when the Knicks looked like they could blow this version out of the building at the start on Tuesday night it seemed like a chance to rid the ghosts of the past. Instead, the Knicks found themselves in just another nightmare.

An early 14-point lead disappeared and the Knicks were overwhelmed by Jaylen Brown, who poured in 15 of his 42 points in the third quarter as the Celtics turned a tight game into a celebration, winning, 123-117, in front of their fans still smarting from the Knicks’ postseason comebacks and ending the run for the group that had won a title.

The Knicks’ efforts to salvage this just kept falling short as Jalen Brunson endured his worst shooting performance of the season, connecting on just 6 of 21 from the floor and only getting to the line for three free throws. He finished with 15 points.

“I saw them pick up their intensity,” Brunson said. “I feel like everything shifted at the end of that first quarter and momentum kind of got on their side and they played really well in that second quarter and throughout the third. I thought we played decent in the fourth as a team, enough to give us a chance. But throughout the game I just didn’t help at all.”

“Things like that happen,” Karl-Anthony Towns said of Brunson. “It’s 82 games in the season and he’s one of the best players in the NBA. So things happen. He didn’t lose his mojo. We know who he is, what he does. So he’s going to be all right. I expect him to bounce back like he’s been doing all season.”

Mikal Bridges led the Knicks with 35 points and Towns added 29.

“We can’t get bored with what’s working, what’s winning basketball,” said Josh Hart, who had 19 points, 11 in the first quarter. “I felt like we got bored doing that. And then we started doing whatever, playing bad offense, giving up anything defensively. So we’ve got to make sure we’re locked in on making sure the success of the team is the No. 1 objective.

“I mean, it’s human nature sometimes when you get those big leads. Now you’re up 15, up 20 sometimes, let me figure out a way to score, how to get mine. Not in a bad way. That’s human nature. We’ve got to try to combat that.

“We’ve got to make sure even when we get up 15, we get up 20, we’re continuing to push the pace, continuing to play fast, continuing play our basketball. I think it’s frankly just kind of stupidity to play one style of basketball, get a 15, 20-point lead and then abandon what got you the lead. We’ve got to make sure we continue to focus on that and build off of it.”

This was the Knicks first time back here since May when they’d pulled off a series of upsets, the Knicks couldn’t help but think back.

The Knicks had three days off before Game 1 of the Eastern Conference semifinals arrived here last season, but in all of the meetings and planning, they never considered that the team’s moment would come by the worst imaginable situation.

TD Garden was going wild, Lucky the Leprechaun was leading cheers and dancing around the floor and the Knicks were 20 points down against the defending champions after being swept in the regular season. You head to the locker room amid the deafening taunts and you have a choice.

The Knicks chose to make this their moment. Maybe chose is not the right word.

“That was not our strategy. We did not big brain that,” Towns joked after the morning shootaround. “I know Thibs [Tom Thibodeau] is a madman with an amazing IQ. That was not one of the ideas. I think that Game 1 showed all the improvements that we made not only as players, as physical talents, but you know, mentally.

“Last year we were such a mentally tough team that nothing bothered us or wavered us. And the 20-point deficit against the champs and being in their home, that didn’t matter to us. We keep fighting [until] the horn goes off.”

When Tuesday night’s game began, the Knicks seemed poised to declare it a new year, jumping out to a 14-2 lead in the opening 2:29 and were ahead by 11 points after one quarter. The margin was 39-25 with 10:28 remaining in the half after a bucket by Towns, but that was when the highlights ended for the Knicks.

In a span of 8:03 in the second period the Celtics went from 14 down to ahead by seven with a 31-10 run, taking a 58-52 advantage into the second half.

The Celtics’ lead grew to 18 entering the fourth quarter and the Knicks were still down 13 as they mounted another rally, this one coming when Bridges was fouled by Hugo Gonzalez attempting a three and it was ruled a flagrant. He made all three shots and the Knicks kept possession. Towns grabbed an offensive rebound and converted a layup, drawing a foul for a three-point play. After the Celtics missed, Bridges drained a three and the Knicks had cut the deficit to just 102-99 with 6:28 to play. In a span of 45 seconds the Knicks outscored the Celtics 10-0.

But a Josh Minott three out of a timeout followed by a pair of follows by Jordan Walsh pushed the lead back to 109-101. With Boston clinging to a five-point lead with 2:54 left, Brown went to the line for his first points of the fourth quarter, hitting one of two.

Bridges delivered a three on the other end and the Knicks were within one possession again.

After a Bridges three, Brown threw the ball away with 24.8 seconds left and after a Knicks’ miss, Deuce McBride and Walsh tied up. The Celtics won the jump ball and called timeout with 12.8 seconds left. A Derrick White layup off the inbounds put it away.

Steve Popper

Steve Popper covers the Knicks for Newsday. He has spent nearly three decades covering the Knicks and the NBA, along with just about every sports team in the New York metropolitan area.