Dwyane Wade added 28 points as the Heat moved closer to vanquishing the defending Eastern Conference champions by taking a 3-1 lead in the best-of-seven series.
Game Five is on Wednesday in Miami where the Heat will attempt to finish off the Celtics.
“What we’re going to face on Wednesday will be our greatest challenge of this season,” said Heat coach Erik Spoelstra. “To put away a champion will be the toughest thing we’ve had to do to this point.”
In last season’s playoffs, Boston eliminated James and the , and Wade and the Heat on their way to the NBA Finals, but the Celtics are finding themselves overpowered by Miami’s new partnership.
Chris Bosh, who signed with Miami along with James in the summer to form a “Big Three” with Wade to challenge Boston’s reign, added 20 points and 12 rebounds including a crucial tip-in with 24 seconds left in OT to give Miami a 95-90 lead.
In a see-saw fourth quarter, the Heat held the Celtics to just 13 points to force the extra session as Paul Pierce missed a potential game-winner as the buzzer ended regulation time.
Miami scored the first six points of overtime to put the veteran Celtics on their heels.
Pierce finished with 27 points and Ray Allen chipped in 17 for Boston.
(Writing by Jahmal Corner in Los Angeles, Editing by Larry Fine)