The defending NBA champions had lost eight of their previous 10 games. That included three road losses in three nights before a welcome two-day break leading into consecutive home games against the league's two worst teams.
Rodrigue Beabuois, who also had a couple of acrobatic plays to keep balls from going out of bounds, added 19 points. He had five in a row in less than a minute early in the fourth quarter when the Mavs had a 7-0 run to go up 92-79.
Trevor Booker had 20 points and 12 rebounds for the Wizards (9-32).
The only team with fewer wins than Washington is Charlotte (6-34), which plays in Dallas on Thursday night before Southwest Division-leading San Antonio is in town Saturday night.
Jason Terry's short jumper started the clinching run early in the fourth quarter, Beaubois quickly followed with consecutive baskets.
Beaubois made a 12-footer, then followed up a Terry miss with another basket and extended his personal run with a free throw on the next possession with 8½ minutes left.
After being called for a foul against Nick Young that led to two free throws and got the Wizards within 70-68 with 4:21 left in the third quarter, Beaubois more than made up for that on the next possession.
Shawn Marion's crosscourt pass appeared headed out of bounds when Beaubois leaped up near the sideline to grab it. While still in the air, Beaubois passed the ball to Vince Carter for a 3-pointer.
Beaubois had another nifty save late in the first quarter after Young stole the ball from Nowitzki. Young took off on a breakaway, but Beaubois hustled back and stripped the ball under the basket. He then grabbed the ball and managed to keep his feet up in the air above the baseline while throwing the ball out to Terry.
When the ball got back to the other end, Beaubois hit a long jumper right in front of the Mavericks bench for a 27-26 lead after the first quarter.
Dallas went ahead to stay in the second quarter, when they shot 82 percent (14 of 17 from the field). They ended the half with a 10-3 run for a 60-51 lead.
That half-ending run came after Nowitzki, who had made his first seven shots, missed a 3 from the top of the key with 2:55 left in the half. But he had a 17-footer and two free throws in the final 44 seconds, giving him 20 points in the first half. He finished 10-of-14 shooting overall.
John Wall had 18 points for the Wizards, while Jordan Crawford and Young had 15 each.
Carter added 14 points for Dallas.
NOTES: Dallas scored 60 points in the first half for the fourth time this season, the first in 18 games — since 64 against Denver on Feb. 8. ... Washington is 3-16 on the road, including six losses in a row. ... Nowtizki had a four-point play with 5 minutes left in the third quarter. After Nowitzki got fouled making a 14-foot jumper, Crawford was called for a technical foul. Nowitzki made the technical free throw, then the freebie for being fouled for a 68-56 lead.