Nowitzki has scored at least 30 in his last three games. The Mavericks won their fifth straight game as they held the Clippers to less than 90 points for the ninth time this season.
The Clippers have lost 12 of 15 games since starting the season 6-4.
Chris Kaman scored 24 points and grabbed 19 rebounds for Los Angeles. It was his 21st double-double of the season and his 11th straight in December.
Dallas led by 12 at the half, but Los Angeles opened the third on a 15-6 run.
Richie Frahm hit a 3-pointer to bring the Clippers within 60-57.
The Mavericks answered as Harris drove for a layup, then stole the ball from Tim Thomas and finished with another hoop to put Dallas ahead 64-57.
Nowitzki hit a jumper to extend the lead to nine. After a Kaman basket, Josh Howard scored five straight points to put Dallas on top 71-59.
Howard scored 15 points, Jason Terry had 14 and Jerry Stackhouse added 10 for the Mavericks, who improved to 13-2 at home.
Cuttino Mobley had 13 off the bench for the Clippers.
Los Angeles got within 88-81 on Dan Dickau's layup midway through the fourth.