Dallas hit its first four 3-pointers to open overtime. The Mavericks rallied from a six-point fourth-quarter deficit after leading by 17 in the first half, and Nowitzki scored 14 points in the fourth and seven in overtime.
The Mavericks have beaten the Celtics seven straight times, 11 of 12 and six straight at American Airlines Center.
The Celtics had a three-game winning streak snapped.
The Mavericks led 17-2 after 8 minutes, during which time the Celtics hit only 1 of 15 shots. Boston then sank 12 of 15 field goal attempts to pull within 40-31 with 7:16 to play in the half. The Mavericks’ 8-0 run put them ahead 52-39 at halftime.
The Mavericks led by 16 early in the third quarter only to have the Celtics outshoot them 55 percent to 29 percent during the period and take a 72-70 lead going into the final quarter.
Boston led 86-80 with 5:48 remaining before Dallas went on a 10-1 run to move ahead 90-87 with 2:47 left.
Celtics: They recalled forward Jordan Mickey from Maine of the Development League. Mickey will join the team for a home game Friday night against Chicago.
Mavericks: Nowitzki entered averaging 25.9 points in 32 previous games against Boston, his highest average against any NBA opponent.