Nowitzki scored 20 points to lead the Mavericks, who have won three out of four since losing their first three games of the season.
Lamar Odom has his best game in a Dallas uniform, with 15 points and five rebounds in 22 minutes. He had not scored more than eight points in a game since being obtained in a trade with the Los Angeles Lakers prior to the season.
Jason Terry added 18 points, helping Dallas build as much as a 21-point lead early in the fourth quarter.
Dallas was having a hard time putting away the Suns in the third quarter when Nowitzki hit a layup with 7:56 to go in the period.
Roddy Beaubois then stole the Phoenix inbounds pass and got it to Nowitzki for another quick layup. Nowitzki was fouled on the shot and his free throw gave the Mavericks a 62-49 advantage with 7:48 remaining.
Marcin Gortat scored 22 points and had 10 rebounds for the Suns, who lost for the fourth time in six games to start the season.