The Pacers held only a five-point lead with 4 minutes remaining, and then closed the game on a 12-4 run that lifted their record 5-2. Boston had a four-game winning streak snapped.
Boston scored only 25 points in the first half, making 3-of-18 shots from the field during an 11-point second period.
The Celtics still trailed by only eight at the break, but their shooting performance improved only slightly during the final 24 minutes. Ray Allen led Boston with 23 points.
Indiana concluded a four-game road trip with a 2-2 record and won in Boston for the first time in eight tries.