Garnett did get involved, scoring 24 points many of his baskets off lobs into the paint and grabbing 11 rebounds to lead Boston to a 101-91 win over the Heat on Friday night that cut Miami's lead in the best-of-seven series to 2-1.
Paul Pierce added 23 points and Rondo followed his Game 2 performance with 21 points and 10 assists to help the Celtics avoid falling into a 3-0 hole after dropping the first two games in Miami.
Game 4 is Sunday night in Boston.
"They defended their home court," Rondo said. "In a couple of days, we'll do the same."
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 went on a 15-0 run to turn a six-point deficit into a nine-point lead.
The Celtics extended it to 24 early in the fourth quarter before Miami cut it to 95-87 with help from three 3-pointers by Mike Miller. But James had a turnover and missed a 3-point attempt in the last 2 minutes to squelch the Heat's hope of a comeback.
"You're trying to fight back the whole time," said James, who scored 16 points in the first quarter but just four with one rebound and one assist in the fourth. "We made a run, but it was too much."
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 1:39 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 Game 2, in which he played every second of regulation and overtime, Rondo was 9 for 16 from the field and grabbed six rebounds. Rivers said there was little he wanted his point guard to change.
"I'm like a pitcher throwing a no-hitter: you stay away from that joker," Rivers said. "The guy scored 44 points, what can I possibly tell him?"
Mostly: Get the ball to Garnett.
With Garnett posting up underneath the rim, Boston outscored Miami 58-46 on points in the paint.
"He (Rivers) kept preaching to just throw it up to him," Rondo said. "They went small, and no one can jump as high as Kevin. He stood up to the rim, and he went up and got most of them."
Marquis Daniels led Boston's reserves 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.
The Celtics center, appearing rejuvenated during these playoffs at the age of 36, got called for another technical foul for a violent elbow but otherwise seemed to be enjoying himself. While waiting to inbound the ball in the second quarter, he high-fived a young child sitting courtside in a No. 5 Celtics jersey.
At the other end, after behind slammed hard to the court by Udonis Haslem, Garnett gingerly rolled over onto his stomach before extending his arms to ease himself off the court. Down and up he went, pushing off the floor on his knuckles eight times for some postseason pushups.
"I'm getting crap about my form, but I want people to know it's because it was on my knuckles," Garnett said. "That's old school. My uncle taught me to do pushups on my knuckles. That's some Army-Navy stuff."
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 a 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. ... Miami was 10 for 20 from the free throw line.