Philadelphia's season-saving victory was far from pretty, but they avoided elimination with a gritty effort to tie the best-of-seven series at 3-3 and set up the decider in Boston on Saturday.
"I think it's going to be crazy, especially being there in Boston," said 76ers point guard Jrue Holiday, who led Philadelphia with 20 points.
"We need to go in there and get this win. I'm looking forward to it."
Elton Brand added 13 and 10 rebounds for Philadelphia, who are on the brink of springing another postseason upset after eliminating top seeds Chicago in the opening round.
Boston's Paul Pierce recorded 24 points and 10 rebounds while Kevin Garnett had 20 and 11 but no other Celtics player scored more than nine and they finished with just 33 percent shooting from the field.
"I thought they had a lot of energy form the building. They just outplayed us," said Celtics coach Doc Rivers.
"We played random a lot. We have to do a better job offensively."
Boston took a 36-33 lead during a sluggish first half but fell behind in the second half.
The 76ers led by four going into the fourth quarter but pulled away with an 8-1 run to seal the win.