The Capitals, one of two teams without a loss in the NHL this season, improved to 6-0. Detroit, which was idle on Thursday, also has an unblemished record in four games.
Vokoun surrendered the game's first goal, coming on a wrist shot by Claude Giroux with 5:35 to go in the opening period. It was the fifth goal for Giroux in the young campaign.
Before the period was over, however, Washington had bounced back to take a 2-1 lead on goals by Mathieu Perreault and Ovechkin. There were only 12 seconds left in the opening period when Ovechkin put the Capitals in front for good.
Sean Couturier put a slap shot past Vokoun with 15 seconds left in the contest.
Ilya Bryzgalov gave up all five Washington goals on 28 shots.