Jason Calliste had 17 points for the seventh-seeded Ducks (23-8). Mike Moser added 13 points and Dominic Artis chipped in 10. Oregon takes on second-seed UCLA in the next round.
Angus Brandt finished with 20 points while Roberto Nelson logged 19 for the 10th-seeded Beavers (16-15). Hallice Cooke registered 12 points and eight boards and Devon Collier netted 11 points.
Oregon shot 43.8 percent from the floor, including 5-of-10 from 3-point range, in the first half, but led by a score of only 41-40 at the break. OSU drained 73.7 percent of its field goal attempts, but took 13 fewer shots that Oregon.
The Ducks were on fire in the second period as they connected on 80 percent of their field goal tries. With 14:12 left in the game, the Beavers were up one but Oregon went on a 20-6 run to bust the game open and cruise to victory.
Oregon's bench outscored the Beavers' reserves 46-6.