LeBron James scored 34 points for Miami, while Dwyane Wade contributed 18 and Mario Chalmers had 14. Mike Miller scored 11 points, all of which came in the second half Friday night.
The 101 points was the most Miami has given up in regulation in the playoffs so far. The Heat gave up 99 points in the first four periods of Wednesday's Game 2 win.
Kevin Garnett led Boston with 24 points on an efficient 10 of 16 shooting, adding 11 rebounds. Paul Pierce scored 23 and Rajon Rondo added 21 points and 10 assists.
But the biggest difference-makers on the Celtics may have been bench players Marquis Daniels and Keyon Dooling, who combined for 16 points and "knocked us back on our heels" with their defense, in the words of Heat coach Erik Spoelstra.
Miami jumped out to an early first-quarter lead behind 16 points by James, but Boston closed on an 8-0 run to make the score 30-28 at the end of the quarter. Then the Celtics scored the first 7 points of the second quarter to extend their lead.
With Daniels and Dooling in for Boston, Miami all of a sudden found itself without any open paths to the lane. Instead, the Heat settled for its subtle kryptonite: mid-range jump shots attempted just before the shot clock expires. The Heat went 7:10 without scoring in the first and second quarters, and nearly 10 minutes without converting a jump shot. Miami attempted nine shots outside the paint in the second quarter, and missed eight of them.
Boston led 55-42 at halftime, with nearly half of Miami's points coming from James. Dwyane Wade was just 3 of 9 in the first half, still stumped by the Celtics' double teams. The Heat bench was almost nonexistent, going 1 of 4 with just 6 points.
Miami came out of halftime with no urgency, allowing Boston to score 30 points and widen its lead to 22 points. For the quarter, James had 10 points on 5 of 6 shooting, while the rest of team went 5 of 15 with 11 points.
The Heat picked up steam in the third quarter, riding an 11-0 run to whittle down Boston's lead to as little as 8, but that was too little, too late.
The Heat struggled from both the 3-point line and the free throw line, going 5 of 17 from downtown and just 10 of 20 from the charity stripe. Miami is now charged with regaining momentum when the series resumes in two days.
Game 4 will tip off in Boston at 8:30 on Sunday night.