Nowitzki was 10-of-14 from the field and grabbed eight rebounds.
Howard was 8-of-15 from the field. He learned earlier in the day that he has been suspended by the NBA for the first two games of the regular season for his role in a fight with Sacramento's Brad Miller on Tuesday night.
Brandon Bass had 18 points and 10 rebounds, Devin Harris scored 17 points and Maurice Ager added 14 for the Mavericks (3-3), who led 93-63 after three quarters.
Flip Murray had 22 points and Rodney Stuckey added 15 for the Pistons (3-3).
The Pistons missed their first six shots while Dallas opened the game 6-of-11 from the field and took a 30-21 lead after one quarter.
Dallas went on to a 63-46 halftime lead behind Nowitzki's 16 points while Harris had 14.
The Mavericks have two preseason games left before opening at Cleveland on Oct. 31.
Detroit has two exhibition games remaining before starting the regular season at Miami on Nov. 1.