That set up the game-winner for Marleau, who swerved toward the net, went to his forehand and put a shot past the stick of Philipp Grubauer.
Tyler Kennedy scored in regulation for the Sharks, who notched a sixth straight win against the Capitals and 17th in 18 meetings dating to 1999-2000.
Ovechkin netted his 33rd goal of the season and Grubauer stopped 28-of-29 shots for the Capitals, losers of two straight.
Notable deaths of 2014 [PHOTOS]
Julius Randle breaks leg during NBA debut