The Wildcats (6-2, 4-1 Pac-10) added rushing scores by Keola Antolin, Nick Booth and Taimi Tutogi, and William Wright scored on a punt return.
Nick Foles completed 2-of-19 passes for 136 yards and a touchdown. Alex Zendejas added field goals from 21 and 26 yards.
Marshall Lobbestael went 7-of-11 for 103 yards and a touchdown for the Cougars (1-8, 0-6), who have lost six in a row.
Jared Karstetter's 64-yard touchdown reception in the fourth quarter accounted for Washington State's score.