BOSTON -- The way things have been going for the Portland Trail Blazers this season, it would have been easy for them to mail in Saturday's end to a four-game road trip, hop on their charter and fly home.

But that didn't happen.

"That was a huge win, especially on this trip losing the first three, being tough enough mentally and physically, too, being the last game," Damian Lillard said after scoring 25 of his 28 points after halftime, seven in overtime, as his Blazers topped the Boston Celtics 127-123.

"It was probably the toughest one on the trip, back-to-back, five o'clock game," said Lillard. "We showed some heart. We showed some grit to go to overtime."

Portland won despite 41 points by Boston's Isaiah Thomas, including 21 in the fourth quarter and overtime as he continued his torrid scoring run.

It was Boston's second straight home loss, both to teams with losing records.

"I told the guys in there ... whatever their record is, 19-27, we all know they're not a 19-27 team," said Celtics coach Brad Stevens, whose team (26-17) lost to the 18-24 New York Knicks Wednesday. "This is a team that was a fourth or fifth seed in the playoffs last year."

Lillard, who also had seven assists, scored six points late in the fourth quarter and then scored on a jumper, an old-fashioned three-point play and two free throws in OT. He iced the game with foul shots with 1.9 seconds remaining.

CJ McCollum, Lillard's running mate in the backcourt, scored 26 of his 35 points in the first half.

With the Celtics down three and 10.8 seconds left in regulation, Boston called a timeout and Terry Rozier then drilled home a 3-pointer from the top of the key with 8.2 seconds remaining.

After a Portland timeout, Lillard went one-on-one with Marcus Smart and missed a jumper as time expired.

Meyers Leonard scored a season-high 17 points and Al-Farouq Aminu had 13 points and seven rebounds, both off the Portland bench. Mason Plumlee had 10 points, 11 rebounds and eight assists and former Celtic Evan Turner, making his first return to TD Garden after spending two years in Boston, had 12 points, four rebounds, four assists, two blocked shots and some strong defense on Thomas late.

"We're definitely taken our hits and our losses," said Plumlee. "But it's a good win, it's just one win and something to feel good about going home (for a five-game homestand)."

The Celtics, playing without injured Avery Bradley, got 17 points apiece from Al Horford (nine rebounds, five assists) and Marcus Smart, 16 from Jae Crowder (13 in the first half), 15 from Terry Rozier and 10 points and eight rebounds from Kelly Olynyk.

Boston turned the ball over a season-high 21 times after a franchise-low three Wednesday, Stevens calling that, "Huge. Huge. I thought we were a little too loose with the ball at times."

Bradley was out for the second straight game, the sixth in the last seven. He was needed Wednesday night, when Derrick Rose scored 30 for the Knicks, and he was needed again Saturday. He is expected to be out another week with a sore Achilles.

Thomas, who has scored at least 20 points in 27 straight games (and not done it only once this season), had 15 points in the second quarter and the Celtics made 13 of 18 shots from the field and led by nine at the break. He remains the league's leading fourth-quarter scorer at just over 10 points per game.

But the Blazers (3-2 in overtime this season) used two 11-0 runs in a 32-point third quarter as Lillard, who had only three in the first half, scored nine points and was 4 of 7 from the floor.

NOTES: Boston outrebounded Portland 47-37, and it was the first time all season the Celtics lost when not losing the boards battle (12-1). ... In addition to missing G Avery Bradley, the Celtics were also without F Jonas Jerebko (illness), leading to almost 13 minutes of playing time for Jordan Mickey (two points, three rebounds). ... The Blazers were without F Ed Davis (wrist). ... Portland G/F Evan Turner, who spent the last two seasons with the Celtics, returned. Talking about Boston coach Brad Stevens before the game, Turner said, "He definitely gave myself and a lot of guys in that locker room, he kind of helped their career and re-energized it." ... Portland has two Massachusetts players, F Noah Vonleh (Haverhill) and G Pat Connaughton (Arlington). ... The Blazers open a five-game homestand against the Los Angeles Lakers on Wednesday. The Celtics are at Washington on Tuesday. The last time the teams played, on Jan. 11, the game ended with a disagreement on the floor that had five police officers standing in the hallway between the locker rooms. ... Boston G Isaiah Thomas received an NBA Assist award before the game.