Tracy McGrady had 21 points and eight assists to lead a balanced attack Wednesday as the host Detroit Pistons notched a 104-92 upset victory over the Boston Celtics, who lost Kevin Garnett to a leg injury.

Garnett was injured while dunking late in the first quarter. He was limping badly on the right leg and committed a foul to stop the game. X-rays were negative and Garnett is scheduled for an MRI on Thursday.

Meanwhile, the Pistons (11-21) were 10-of-15 from 3-point range and forced the Celtics (24-6) into 21 turnovers while pulling off one of their most impressive victories of the campaign. McGrady made 7-of-11 shots while making his third start of the season in place of Rodney Stuckey.

Both teams were without their starting point guards. Stuckey sat out with a stomach virus and Boston's Rajon Rondo missed his sixth straight game with an ankle injury.

Tayshaun Prince scored 18 points, Charlie Villanueva added 14 on four 3-pointers and Ben Gordon and Austin Daye had 12 apiece for Detroit.

Paul Pierce had 33 points, eight assists and four steals and Ray Allen and Glen “Big Baby” Davis added 12 points apiece for Boston.