Game 4 is Sunday night in Boston.
Paul Pierce scored 23 points for Boston.
LeBron James scored 34 points, but the NBA MVP and the rest of the Heat went cold during a 7-minute stretch at the end of the first quarter and the beginning of the second, when Boston outscored them 15-0 to turn a six-point deficit into a nine-point lead.
James scored 16 points in the first quarter but had just four points with one rebound and one assist in the fourth, when Miami cut a 24-point deficit to eight. Mike Miller hit consecutive 3-pointers during an 11-0 run that cut the deficit to 95-87.
Miami still trailed by eight points, with the ball, when Dwyane Wade missed and Ray Allen grabbed the rebound, sending Rondo on a fast break that made it a 99-89 with 99 seconds to play. James threw the ball away underneath, then missed a 3-point attempt the next time down – one of only four shots he took in the fourth quarter.
Pierce found Garnett for a long jumper at the other end, and the teams began emptying their benches.
Coming off his 44-point effort in the Game 2 loss in Miami, in which he played every second of regulation and overtime, Rondo was 9 for 16 from the field and grabbed six rebounds.
Marquis Daniels led the Boston bench with nine points and five rebounds in 18 minutes.
Wade scored 18 points and Mario Chalmers had 14 points and six assists for Miami. Shane Battier was scoreless, missing all six shots, and Ronny Turiaf had three points while tangling with Garnett under the basket for much of the game.
Wade was 9 for 20 from the field and did not shoot a free throw in the game. James, who shot 24 free throws in Game 2, making 18, was 1 for 5 from the line.
James hit seven of his first nine shots, before making one of the next six. That helped Boston score the last eight points of the first quarter and the first seven of the second to turn six-point deficit into a nine-point lead. Much of it came with Keyon Dooling and Daniels on the court for Boston.
Notes: During the first timeout, the Celtics acknowledged Boston Globe columnist Bob Ryan, who is retiring this summer. GM Danny Ainge was one of the first to stand and applaud. ... K.C. Jones, who was celebrating his 80th birthday, and fellow Celtic great John Havlicek were in the crowd.