Joe Thornton drew an interference call on Edmonton's Theo Peckham early in the final frame and the Sharks made the Oilers pay.
Joe Pavelski made a diving cross-crease pass while falling that Marleau one-timed past a startled Nikolai Khabibulin, breaking a 2-2 tie and boosting the Sharks to a win in the first contest of a six-game homestand.
The Oilers, meanwhile, continued to struggle, losing for the seventh time in 10 games.
Khabibulin finished with 34 saves.
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