Nowitzki's jumper with 8:26 to play gave Dallas an 85-84 lead and ignited the critical surge that brought the Mavericks their second straight victory.
O.J. Mayo led the Mavericks with 28 points and had five assists. Vince Carter scored 17 points off the bench and Nowitzki had 16. Both teams made 10 3-pointers, but Dallas needed just 20 shots to do so and Portland made 30 attempts from beyond the arc.
The win was the 500th as Dallas coach for Rick Carlisle.