The 342nd meeting between the rivals was their first in the Pac-12 tournament and carried plenty of implications for Oregon's NCAA tournament chances.
The defending tournament champion Ducks (23-8) came through after a shaky start, relying on their depth and superb second-half shooting to earn a spot in Thursday's quarterfinals against second-seeded UCLA.
Jason Calliste scored 17 points and Oregon made 16 of 20 shots in the second half for its eighth straight victory. The Ducks outscored Oregon State, 46-6, off the bench and made 10 of 16 from three-point range.
Angus Brandt scored 20 points and Roberto Nelson had 19 in what was probably their final game with the Beavers (16-15).
After opening Pac-12 play at 3-8, the Ducks have looked more like the top-10 team they were at the beginning of the season, reeling off seven victories to close out the regular season. Oregon picked up a big one to close the season, beating then-No. 3 Arizona at home to boost their NCAA tournament profile but still was lingering around the bubble heading into the Pac-12 tournament.
The Beavers are not only Oregon's biggest rival, they beat the Ducks in January and their only shot at reaching the NCAA tournament was to win the Pac-12.
The Ducks led, 41-40, at halftime after scoring 15 points on Oregon State's 10 turnovers.
Utah 67, Washington 61: Delon Wright scored 15 points and Jordan Loveridge had 13, helping the Utes hold off the Huskies in the opening round.
Utah (21-10) dominated the first half before Washington rallied in the second to set up a close finish.
Dakarai Tucker put the Utes ahead, 63-60, on a three-pointer from the corner with 37 seconds left and Brandon Taylor made two free throws after Washington's Nigel Williams-Goss missed a potential tying three-pointer.
Utah moves on to face top-seeded Arizona in the quarterfinals on Thursday.
Washington (17-15) fought back after trailing by 12 in the first half but couldn't get shots to fall down the stretch.
Stanford 74, Washington State 63: Chasson Randle scored 22 points as the Cardinal (20-11) defeated the Cougars (10-21) in the last game of the day.
Stanford (20-11) shot 58 percent against the 11th-seeded Cougars and used a 16-4 run in the second half to take control of what had been a tight game.
Anthony Brown and Josh Huestis scored 12 points each for the Cardinal, who face third-seeded Arizona State (21-10) in the quarterfinals on Thursday.
Washington State (10-21) shot well to start both halves, but couldn't sustain it. DaVonte' Lacy scored 25 points and D.J. Shelton finished with 15 points and 11 rebounds for the Cougars, who made five of 18 shots from three-point range.