Damian Lillard had 26 points and 13 assists for Portland. Carmelo Anthony finished with 13 points — including a 3-pointer with 1:08 remaining to help seal it after Boston pulled within two points.
The Trail Blazers improved to 4-0 on their six-game road trip. They entered the game in seventh in the Western Conference playoff standings and are trying to work their way out of the play-in round.
“I think we’re playing better basketball at the right time,” McCollum said. “Understanding the severity of each game — what we need to accomplish heading into the playoffs and what we need to accomplish to get into the playoffs is very important.”
Jayson Tatum scored 33 to lead Boston, which is trying to avoid falling into the play-in round in the final weeks of the season.
“We need to just take the mindset of whether we won or lost, you can’t change that,” Tatum said.
After rallying from 32 points behind to beat San Antonio in overtime Friday night, the Celtics couldn’t produce another comeback against the Blazers, who shot 52% (44 for 85). The Blazers also helped themselves by forcing 18 turnovers and committing only nine.
“I think the biggest thing is I thought we were very aggressive on the ball,” coach Terry Stotts said. “We created turnovers in a variety of ways. But I think the pressure on the ball, our hands and our alertness on the weak side all played a part in it.”
Norman Powell scored 23 points, Robert Covington had 10 and Jusuf Nurkic pulled down 11 rebounds for Portland, which will have six games remaining — including four at home — once the road trip ends after stops in Atlanta and Cleveland.
“Like I was saying before we left on the road trip, on the road trip, what are you willing to do to dig yourself out? How desperate are we willing to go out there and look and be and behave?” Lillard said. “We need to win these games. We need to get stops. We need to have a presence. We’ve got to take a challenge and tonight was pretty much the same thing. “
After the teams went into halftime tied at 71, Portland capitalized on six turnovers in the third quarter and led 103-98 entering the fourth quarter.
Tristan Thompson appeared to put the Celtics back up on a put-back dunk, but the basket was waved off because of offensive interference. The Blazers, who led 107-106 after the call that was widely disputed by the Celtics and their fans, got back-to-back 3-pointers from McCollum and Anthony for a 113-106 lead.
The Celtics stayed within a basket or two and had another chance after Tatum hit a pair of free throws to pull Boston within 121-119 with 1:21 left to play.
But Anthony answered for Portland with a 3-pointer, then sidestepped his way back on defense while waving his arms at Boston’s fans. After a miss by the Celtics, Powell took it the other way for a layup and Portland had a 126-119 lead.
Aaron Nesmith, who scored 16 for Boston, said the Celtics had some difficulties staying consistent on defense.
“In the second half we were able to pick it up, but we’ve got to be able to do it for 48 minutes,” Nesmith said.
Trail Blazers: Lillard led all scorers with 11 points in the first quarter. … Anthony needs 10 points to pass Elvin Hayes (27,313) for No. 10 on the NBA’s career list.
Celtics: G Kemba Walker (left oblique strain) missed his fourth straight game. Coach Brad Stevens said the Celtics hoped to have Walker practicing again by Tuesday and possibly playing again Wednesday at Orlando. … Marcus Smart finished with 11 points, eight assists and eight rebounds before he was ejected with 1:56 left after receiving a technical foul. … Jaylen Brown, a game-time decision because of a right ankle sprain, finished with 16 points and 11 rebounds. … Evan Fournier scored 21.
Trail Blazers: Visit Atlanta on Monday night.
Celtics: Visit Orlando on Wednesday night.