Signed as a free agent just before training camp, Nieuwendyk made his first appearance at the American Airlines Center since being traded to New Jersey in March 2002. He received a warm reception from the crowd of 18,532.
Nieuwendyk, who led the Stars to the Stanley Cup in 1999 with 11 postseason goals, gave Toronto the lead with seven minutes left in the third.
With Pierre Turgeon serving a hooking penalty, Nieuwendyk stationed himself in front of goaltender Marty Turco. With his back to the goalie, he got his stick on Sundin's shot from the right boards and deflected it in for his 512th career goal.
The assist was the first point of the season for Sundin.