Nowitzki was on the bench for most of a key third-quarter stretch as the Mavericks restored a double-digit lead behind by Harris, Brandan Wright and Jose Calderon.
Harris had seven points on a 9-2 run that gave the Mavericks their first 15-point lead, and Wright scored nine of his 14 points in the third. Jose Calderon had four of his game-high 10 assists in the quarter and hit a pair of 3-pointers.
Kyrie Irving had 27 to lead the Cavaliers, who have dropped seven of their last eight.
Anthony Bennett, Cleveland's rookie No. 1 pick averaging just 2.8 points per game coming in, had eight in the second quarter and finished with 11.
Dallas' Monta Ellis started fast after going most of the first half without scoring Friday against Sacramento and finished with 22 points and seven assists.
After missing the first 41 games following offseason toe surgery, Harris had his previous season high of 14 points in three straight games before getting seven in Friday's win over Sacramento.
Harris finally broke the 14-point mark with a pair of free throws, and then assisted on a dunk by Samuel Dalembert that gave Dallas its biggest lead at 106-87.
Dalembert had 18 points — two off his season high — and two blocked shots. Calderon scored 11.
Five days after Cleveland general manager Chris Grant questioned his team's will, the Cavaliers didn't quit. They scored eight quick points and had a chance to make it nine when Jarrett Jack got fouled after making a 3-pointer.
Jack missed the free throw, and the Cavaliers couldn't get the deficit under 10 after that.
Luol Deng scored 18 points, Tristan Thompson had 17 and both had eight rebounds for the Cavaliers, who had seven players in double figures.
Nowitzki, who was averaging 33 points in his previous three games, had 16 in the first half and matched Dalembert with eight rebounds.
Nowitzki scored the last eight points on a 13-2 run that put the Mavericks up 52-39, but he missed his last three shots of the first half as the Cavaliers got back within seven at halftime.
Ellis followed up an 11-point fourth quarter that boosted a rally to beat Sacramento on Friday with 13 points on 5-of-6 shooting in the first half against Cleveland.
NOTES: Mavericks F Shawn Marion missed his second straight game with lingering issues from shoulder and rib injuries. He's missed six games since getting hurt Jan. 7 against the Lakers. ... Cavaliers C Anderson Varejao started after being questionable with a left knee injury. He recorded both the 4,000th point and 4,000th rebound of his career. ... Rookie G Shane Larkin was back with the Mavericks after a one-game stint with their D-League affiliate in suburban Dallas. His playing time has dipped significantly since Harris returned from offseason toe surgery. ... Ellis had six of Dallas' 13 turnovers after ending a 114-game streak with at least one turnover by going without one against Sacramento. The Mavericks had a season-low four as a team against the Kings