Boston held only a one-point lead at halftime, and then broke the game open in the third period by holding the Warriors scoreless for a 4 1/2-minute stretch.
Corey Maggette had 23 for Golden State.
Boston shot 52.5 percent from the field but made only 17-of-27 foul shots.
The Warriors lost their third in a row and have won on the road just once this season in seven outings.
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