Eddie House came off the bench to score a season-high 20 and lead visiting Miami.
House hit two free throws with 8.3 seconds left to clinch the game after a tight fourth quarter that featured seven ties.
The Sixers missed three off-balance shots on their final possession with less than 30 seconds to play, including a 3-point attempt by Eric Snow that would have tied the score.
Five Heat players were in double digits. Alonzo Mourning had 16 and Rod Strickland 14. House's previous season-high was 17.
Allen Iverson scored 38 for Philadelphia.
Miami stayed within striking distance of the Hornets for the final playoff spot in the East. The Sixers fell two games behind Orlando for the fifth spot.
WIZARDS: Michael Jordan was activated from the injured list and returned to action in a late game against the Nuggets.
Jordan was expected to miss a month after surgery on his right knee Feb. 27, but participated in a morning shootaround. "I think he feels pretty good," coach Doug Collins said.