Nowitzki started Sunday's home game against San Antonio following a planned four-game absence to rest his sore right knee and work on his conditioning. Dallas (13-8), which went 3-1 without the reigning NBA finals MVP, prevailed 101-100 in overtime Sunday.
Jason Terry had a season-high 34 points - including four in the last 42 seconds of the extra session - to lead the Mavericks to their fifth win in six games. Vince Carter added 21 points as Dallas took over first place in the Southwest Division.
"It's just the will to win when the game is on the line," Terry said. "When my team needs me the most, I'm going to come through regardless of what's going on the entire night. Fourth quarter is winning time."
Nowitzki finished with 10 points on 5-of-14 shooting but had a season-high 13 rebounds during his 38 minutes. Jason Kidd, meanwhile, missed the game after straining his right calf in the opening minutes of Friday's 116-101 victory over Utah.
Coach Rick Carlisle said Sunday that his point guard would be sidelined at least a week and possibly longer. His absence comes at an inopportune time for Dallas, which is in the middle of a stretch of five games in seven days.
"I felt like I got kicked in the calf," said Kidd, who was told by a team trainer that nobody had actually hit him. "I'm happy it was just a strain."
The Kidd-less Mavericks will try to earn another win by taking advantage of the Suns' recent shooting struggles. Phoenix (7-12) has shot worse than 37.5 percent in three of its last four games but snapped a three-game skid with an 86-84 home win over Memphis on Saturday.
"We've got to do what we can to try and win at home," Suns coach Alvin Gentry said. "We'll continue to work and continue to try and get better. That's the only thing you can do."
Jared Dudley made two free throws with 3.3 seconds remaining to win Saturday's game for Phoenix, and finished with a season-high 20 points. Nash scored a team-high 21, but limped off the court with a bruised left thigh after colliding with the Grizzlies' Marc Gasol in the final seconds.
The point guard, who spent six seasons with Dallas from 1999-2004, is now seven assists shy of topping Kevin Johnson's Phoenix franchise record of 6,518.
"It's just frustrating," Nash said. "Hopefully it will settle down by Monday. I'm optimistic I can play on Monday, but you never know."
Nash's absence would deal a blow to Phoenix's attempt to earn its first win over Dallas since Jan. 28, 2010.
Nowitzki scored a team-high 20 points during a 98-89 home victory over the Suns on Jan. 4 but sat out the rematch last Monday, a 93-87 Mavericks win in Phoenix. Shawn Marion had a season-high 29 points in that game for Dallas.