It was the third win for the Southwestern Athletic Conference over the Pac-12 in the inaugural Pac-12/SWAC Legacy series, after Grambling beat Colorado last week and Texas Southern downed Arizona State.
Douglas was 11 of 20 from the field and Gambrell 6 of 15 for Prairie View (3-0).
The Panthers led by 21 points with 7:28 remaining in the second half before Washington State closed on a 16-6 run.
Douglas scored 17 points in the first half to help Prairie View build a 41-27 lead by halftime. The Panthers shot 54.8% from the field and held the Cougars to 31.8.
TJ Bamba scored nine of his 16 points in the final six minutes for Washington State (1-2). Kymany Houinsou added 10 points.
The Cougars play Eastern Washington on Monday.
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