Gerhart's score made it 14-7 Minnesota with 9:48 to go in the third period and the Vikings (4-7) hung on to give interim head coach Frazier a victory in his first game since replacing the fired Brad Childress Monday.
Adrian Peterson also scored, carrying the ball six times for 36 yards before slightly hurting his right ankle. Gerhart piled up 76 yards on 22 carries and Brett Favre completed 15-of-23 passes for 172 yards for the victors.
The Redskins (5-6), who lost for the third time in four games, got 211 yards, a touchdown and an interception from Donovan McNabb.
Notable deaths of 2014 [PHOTOS]