The Beavers (4-0, 3-0 Pac-12) intercepted four passes in all.
Sean Mannion piled up 270 passing yards and tossed a TD, and Trevor Romaine booted two field goals for Oregon State.
Connor Halliday completed just just 9-of-20 passes for 81 yards with three interceptions for the Cougars (2-4, 0-3).
He was pulled in favor of Jeff Tuel, who went 11-of-17 for 126 yards and a pickoff the rest of the way.
Andrew Furney registered two field goals for Washington State.
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