Jaylen Brown had 21 points and Jason Tatum added 15 for the Celtics.
Joel Embiid had 30 points and 13 rebounds to lead the 76ers. They shot 29.5% from the field.
Boston led 51-49 at the half, with Embiid carrying Philadelphia with 22 points and 10 rebounds.
The Celtics were able to stay close despite Tatum picking up his third foul near the end of the first quarter and having to sit the entire second quarter. Tatum entered the game averaging 32.5 points on 10-of-17 shooting from 3-point range in the series.
Midway through the third, Walker completed a personal 8-0 run with a fast-break layup and foul on Embiid — his fourth. But Philadelphia didn't fold with its All-Star center on the bench, instead battling back to tie it.
The Celtics entered the game having outscored the 76ers 87-42 from beyond the 3-point arc, but were just 8 of 31 on Friday night. Yet that was better than the 76ers, who were 9 of 39.
Celtics: Daniel Theis picked up his sixth foul with 3:01 left with the Celtics up 92-90.
76ers: Al Horford, who started Game 1, got the start against the Celtics. ... 76ers were 29-2 playing at home in Philadelphia this season, but didn't have the luxury of a home-court advantage playing in the bubble. ... Lost despite outrebounding the Celtics 57-45.
Game 4 is Sunday.