Dallas led by 20 points entering the fourth quarter, but that advantage was cut to just three when Jamal Crawford made a layup with 8 seconds to go.
The Trail Blazers did not even bother to defend Wright as he coasted in for his dunk, but that basket turned out to be critical when Portland's Wesley Matthews hit a 3-pointer just before the buzzer to account for the final score.
It was a key Dallas win in its bid to wrap up a playoff berth. The Mavericks climbed within a game of Memphis for the No. 5 spot in the Western Conference and are now 1 1/2 games ahead of both Denver and Houston, who are tied for the seventh and eighth positions.
Dirk Nowitzki led Dallas with 24 points and Delonte West added 21. Nicolas Batum scored 20 for the Trail Blazers.