The victory allowed the Huskies (20-10, 10-7) to move into a four-way tie for third place in the Pac-12 with just one game remaining. Washington hosts seventh-place Oregon (9-8) on Saturday.
Oregon State (14-15, 6-11), which has not won a conference road game all season, secured 10th place in the final Pac-12 regular-season standings with a trip to Washington State still on the schedule.
After Washington led by as many as 11 points in the first half, the second period featured six ties before Noah Dickerson gave the Huskies the lead for good at 65-64 with a jumper with 6:20 to play.
Two free throws by Stephen Thompson Jr. had the Beavers within 72-69 with still 1:28 to go before Nowell countered with his big shot at the 1:04 mark, extending the Washington lead to five.
Thybulle then stole the ball from Thompson, setting up a Nowell free throw that extended the margin to 75-69 with just 40 seconds left.
Tres Tinkle had a three-point play and a 3-point hoop in the final 15 seconds, but they weren't enough to overcome the Oregon State deficit.
The win not only avenged a 97-94, double-overtime loss at Oregon State earlier this season, but gave Washington a 20th victory for the first time since going 24-11 in 2012. The Huskies' 10 conference wins are their most since going 14-4 in 2011.
Dickerson led all scorers with 25 points for the Huskies, who have gone 6-2 at home in conference play. He hit 10 of his 13 shots.
Nowell, Thybulle and David Crisp added 12 points apiece, with Thybulle and Crisp each connecting three times on 3-pointers. The Huskies shot 8-for-16 on 3-pointers.
Tinkle had a team-high 22 points for the Beavers, who outrebounded Washington 26-17. Tinkle and Drew Eubanks collected seven rebounds apiece.
Tinkle had 29 points in the earlier home win over the Huskies.
Stephen Thompson totaled 19 points, Eubanks 15 and Gligorije Rakocevic 10 for Oregon State.
Washington threatened to run away and hide in the first half, going up by 11 in the late stages before Oregon State rallied to make it 42-37 at the break.
The Beavers then drew even at 44-all on a 3-pointer by Thompson just 2:46 into the second half, setting up the tight finish.
--Field Level Media
Oregon St. | Washington | |
Tres Tinkle 22 | Scoring | Noah Dickerson 25 |
Ethan Thompson 3 | Assists | Jaylen Nowell 4 |
Drew Eubanks 7 | Rebounds | Noah Dickerson 5 |
Drew Eubanks 5 | Free Throws Made | Jaylen Nowell 8 |
Tres Tinkle 2 | Steals | Noah Dickerson 2 |
Drew Eubanks 1 | Blocks | Matisse Thybulle 3 |
Team | Points | FG% | 3PM-3PA | FTM-FTA | Assists | Rebounds | Blocks | Steals | Turnovers |
Oregon St. | 77 | 56.9 | 7-18 | 12-16 | 12 | 25 | 2 | 3 | 14 |
Washington | 79 | 57.1 | 8-16 | 23-30 | 9 | 15 | 4 | 5 | 8 |