Dallas led most of the game, but Paul Pierce hit a 3-pointer — just his second basket of the night — to tie it at 85 with 25 seconds to play. Former Celtic Delonte West dribbled the clock down to about 10 seconds before giving it to Nowitzki. The NBA finals MVP cut to the basket past Garnett and picked up a foul from Brandon Bass while floating the ball into the basket.
The Celtics had a chance to tie, but Rajon Rondo's pass to Ray Allen behind the 3-point line was too low to handle and went out of bounds.
Rondo scored 24 points for Boston and Garnett had 16 points with 10 rebounds. The Celtics have lost two straight since winning four in a row.
Brendan Haywood had eight points and 11 rebounds and reserve Jason Terry scored 18 points as Dallas won its third straight game to improve to 6-5. The Mavericks, who swept Boston last season en route to their first NBA title, have beaten the Celtics three games in a row.
Dallas dominated the first quarter and gave it back in the second, but coach Rick Carlisle's ejection early in the third quarter seemed to turn things around.
Carlisle was called for consecutive technicals just 1:26 into the second half when he ran down the sideline, over midcourt, to protest to the referee. Allen hit the two technical foul shots to give Boston a 47-42 lead, but Dallas scored 24 of the next 30 points to take a 66-53 lead on Terry's 3-pointer with 2 minutes left in the third.
Boston scored the next six points, then opened the third quarter with Keyon Dooling's 3-pointer and a jumper by Bass to make it a four-point game. Dallas led 74-66 before the Celtics rallied to tie it at 77 on Rondo's layup with 6 minutes left. The teams then went on a scoring drought and it wasn't until Ian Mahinmi scored on a putback of Vince Carter's miss with just over 4 minutes left that the Mavericks retook the lead.
Dallas led 84-79 before Pierce, who had two points thus far, made one of two free throws and then made a nice pass to Garnett to set up a dunk that cut the deficit to two points. After West made one of two free throws, Pierce hit a 3-pointer from the right of the key to tie it at 85.
The Celtics missed their first seven shots of the game and nine of their first 10 while falling behind 10-2 less than five minutes in. West had Dallas' first three baskets.
Notes: Pierce played in his 970th career game; his next will tie him with Kevin McHale for third on the Celtics' list. Only John Havlicek (1,270) and Robert Parish (1,106) are ahead of them. .... Celtics F Mickael Pietrus made his season debut, having missed the first two weeks to rehab his right knee after arthroscopic surgery. ... Boston Bruins forwards Tyler Seguin and Brad Marchand watched the game courtside. ... Nowitzki needs three points to reach 23,000.