Garnett grabbed seven rebounds and Rajon Rondo posted a triple-double with 11 points, 10 rebounds and 10 assists for Boston, which improved to 39-14 and leapfrogged the Heat by a half-game in the conference standings.
The Heat, meanwhile, saw their eight-game winning streak snapped.
Chris Bosh scored 24 points and collected 10 boards, LeBron James added 22 points, seven rebounds and seven assists and Dwyane Wade netted 16 points for Miami.
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