The loss, described by Celtics coach Doc Rivers as “self-inflicted,” brought Boston’s five-game win streak to a halt as the Lakers improved to 4-9 away from home this season.
They are 2-2 on their current six-game road trip.
Gasol forced overtime with a put-back basket with less than 10 seconds remaining to tie the score at 82-82 and preserved the win with a shot block on Ray Allen as time expired in OT.
“You just got to play until the clock runs out and that’s what I try to do,” Spaniard Gasol told reporters.
“I’ve been in situations in my career where you just freeze and you just catch yourself looking at the ball and somebody makes a play and you end up losing a game.
“Tonight I’m glad that I was able to continue playing until the end and play a good game for my team.”
Boston held the advantage for much of the first half, leading by as many as nine points but Los Angeles battled back and briefly led before falling back to trail 47-45 at halftime.
The Lakers surged ahead again late in the third quarter and held the lead until a back-and-forth final eight minutes which featured five ties and three lead changes.
“This was an awful game,” fumed Rivers. “If we had won, it would have been an awful game that we won. Give them credit, a lot of that was defense. But I thought a lot of it was self-inflicted.”
Kobe Bryant led the Lakers (15-11) with 27 points and Gasol recorded a double-double with 25 points and 14 rebounds. Andrew Bynum finished with 16 points and 17 rebounds.
Allen led the Celtics (14-11) with 22 points, but scored just three points after the third quarter. Paul Pierce scored all five Celtics points in overtime and 18 overall.
(Reporting by Mike Mouat in Windsor, Ontario. Editing by Alastair Himmer.)