Oregon State pulled away midway through the second half when Gibson hit a pair of 3-pointers and Sydney Wiese added a third, turning a five-point lead into a 12-point advantage with less than five minutes to play.
OSU played at home for just the fourth time over the past two months, having played six road games and five on neutral courts.
Wiese, a freshman point guard, finished with 13 points and dished out six assists. Ruth Hamblin and Jamie Weisner both added 12 points. Oregon State (11-8, 3-4 Pac-12) shot 26-of-61 from the field (42.6 percent) and converted 11 of 25 3-point attempts.
Washington (10-8, 3-4) got 27 points from Kelsey Plum and another 21 from Jazmine Davis, but shot just 36.9 percent (24-of-65).
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