BOSTON — In a change of philosophy by the team captain, Jalen Brunson chose to look at the positive from a negative result.

And the only positive from Sunday’s 118-105 defeat was the third quarter. Otherwise, the Knicks couldn’t compete with the Celtics.

Again.

“Whatever we did in the first, second and fourth quarter doesn’t really matter,” Brunson said. “The third quarter, what we showed was how we can play and how we can compete and how we can — I don’t really care what’s going on, the way we stepped up in the third is how we should play.”

The Knicks indeed showed more fight than the previous game in Cleveland, but they were pummeled in the bookend quarters and trailed by double digits for most of the afternoon.

The encouraging moments — perhaps the most encouraging in all three humbling losses to the Celtics this season — arrived in the third quarter, when the struggling Mikal Bridges was benched for Miles McBride and New York cut the deficit to four points.

For a team searching for belief that it might have a shot against the Celtics in a playoff series, it was the straw to grasp at.

Brunson, who typically focuses on the negative because it fuels improvement, was cryptic about the third-quarter surge, but it felt like there was an underlying message about otherwise playing selfishly.

“We just had a level of not really caring anymore,” Brunson said. “Just all right, we’ve got to go somehow. I mean, from my point of view, that’s what it felt like.”

What did he mean by don’t care?

“Don’t care about, like, me,” Brunson said. “Just try to find a way to win. We’ve done it in the past against other teams, but it’s the first time we did it against this team. We can do it, but we have to do it for four quarters.”

The good times were short-lived for the Knicks. Derrick White hit a momentum-shifting 3-pointer to give Boston a seven-point lead with 11 minutes left. Then Bridges was reinserted, Brunson was sitting for quick rest to start the fourth quarter, Karl-Anthony Towns appeared to hurt his knee and the Knicks reverted to matador defense for several minutes.

They were outscored by 23 points in the 28 minutes played by Bridges, who was acquired for five first-round picks in the summer to combat Boston’s elite wings. He was subbed out with a 21-point deficit and nine minutes remaining in the third quarter after getting hit in the face and believing he lost a contact lens.

Bridges, who didn’t return until 10:45 left in the fourth, said the Knicks can use the loss as a way to get better.

“Just learning,” said Bridges in a brief and unexpansive postgame interview. “I think learning from the third quarter and learn from the other games as well.”

The Knicks (37-20), who have fallen four games behind Boston for second in the East, have been outscored by 63 points in three games against the Celtics while allowing 65 3-pointers on 144 attempts.

“It’s obviously an ongoing process [trying to close the gap on the Celtics],” Tom Thibodeau said. “Their team is a well-oiled machine. They’ve been together for a while and so we have to keep learning and getting better.

“I think the fact that we were able to close that gap to get it to 89-85 in the fourth quarter, that’s where we gotta be better. When we’re in that position, that’s when we gotta be at our best.”

Other than that third-quarter stretch, the afternoon was another Knicks ride on the struggle bus versus the NBA champs.

Within three minutes of tipoff, Thibodeau’s squad was already down by 10. After one quarter, the Knicks had allowed 38 points and trailed by 19.

Jayson Tatum, their tormentor this season, carved the Knicks up early and finished one assist shy of a triple-double with 25 points.

And for the third time this season, the Knicks trailed by double digits for most of a Boston game.

“I feel like we have a lot of work to do,” Thibodeau said, “but I always feel like we have a lot of work to do.”

Until that work is done, the Knicks can’t be considered contenders, regardless of Sunday’s third quarter. They’re too far below the Celtics and Cavaliers to be taken seriously. The matinee at TD Garden was just the latest example.

Thibodeau tried to make some adjustments. He put OG Anunoby, rather than Bridges, on Tatum. It didn’t pay dividends until the second half, when McBride was also on the floor to man the perimeter.

Towns again looked lost trying to defend Boston’s screens, allowing Kristaps Porzingis to pop into countless open treys. Towns caught fire in the third quarter but appeared to aggravate his knee on a dunk attempt, and looked uncomfortable in the final minutes.

The Knicks had no valid excuses. Josh Hart returned from a two-game absence because of a sore knee. He finished an assist shy of a triple-double with 20 points. Anunoby was ineffective and disappeared for much of the day. New York’s lineup from opening night was healthy and on the floor.

And just like opening night, the Knicks left Boston with a decisive defeat. The only difference was a sign of life in the third quarter.

But it wasn’t close to enough.

“We’re not trying to close a gap with the Boston Celtics,” Hart said. “They’re the champs for a reason. They got All-NBA guys, they got All-Stars, they got a heck of a team.

“So we’re not trying to close the gap on them. We’re trying to make sure we get ourselves to where we need to be at the end of the year, and right now, we’re not there.”