Paul George had 16 points and nine rebounds for the seventh-seeded Sixers, who lost Games 3 and 4 at home to fall behind 3-1 in the series before returning to Boston to keep their season alive.
Game 6 is back in Philadelphia on Thursday night, when the Sixers will try to force the series to a decisive seventh game in Boston on Saturday.
In his second game back from an emergency appendectomy, Embiid helped rally Philly from a 13-point, third-quarter deficit.
After scoring 13 points in the second quarter, he added 10 in the third as the Sixers went on a 12-0 run to turn a three-point lead into a 15-point runaway.
Jayson Tatum had 24 points and 16 rebounds for Boston and Jaylen Brown scored 22.