Sami Whitcomb scored 14 points, Laura McLellan 12, and Kristi Kingma 11 to help the Huskies beat the Beavers and extend Oregon State's losing streak to 17 games.
Its second straight victory moved Washington (11-16, 6-11 Pacific-10 Conference) into a tie with Arizona for seventh place with one game left. The Huskies host Oregon on Sunday.
Talia Rhea scored 12 points, Haiden Palmer 10 and Julie Futch nine for Oregon State (9-19, 1-16).
McLellan had 10 of her 12 points in the second half to ignite a 19-5 run after the Beavers had cut the lead to 46-42 with 11:27 remaining.
Regina Rogers scored a three-point play to start the Washington rally before she went to the bench with her fourth foul with 10:46 left. McLellan replaced Rogers and scored three baskets and four free throws to help the Huskies pull away.
The Huskies shot 22 of 28 (79 percent) on free throws. Whitcomb was 9-for-9 from the line and McLellan 4-for-4. The Beavers were 15 of 22 (68 percent) on free throws.
Palmer had 10 points, and Rhea eight to help give the Beavers a 33-32 halftime lead. The game had seven lead changes and seven ties in the first half. Neither team led by more than six.
But Oregon State shot just 20 percent (5 of 25) in the second half compared to 11-for-21 by the Huskies. The Beavers were 2 of 17 on 3-pointers in the game. Rhea missed all eight of her attempts from beyond the arc.
The Huskies were 1 of 7 on 3-pointers as they used their inside game and free throws to get the victory.
The Beavers have not won since they beat Washington State to open conference play Jan. 1. They have lost 16 straight conference games as well as a non-conference game to Cal State Bakersfield.