Roberto Nelson scored four of his 24 points in overtime, including the go-ahead basket with 25 seconds remaining, to lift Oregon State past USC 76-75 Thursday night.
Pe'Shon Howard had a chance to pull USC even after making the first of two free throws with 0.9 seconds left, but missed the second and Devon Collier grabbed the rebound for Oregon State.
Angus Brandt finished with 14 points and Eric Moreland grabbed 10 rebounds and four blocked shots for the Beavers (12-8, 3-4 Pac-12), who trailed 39-36 at halftime.
Byron Wesley led USC (10-11, 1-7) with 23 points as the Trojans lost for the seventh time in eight games.
Tied at 74-74, the Beavers ran an isolation play for Nelson, who started near the top of the lane and then weaved his way through three defenders before laying the ball in off the glass for the game-winning basket.
Oregon State coach Craig Robinson's call for improved defense after Saturday's 87-81 loss at Washington didn't carry over to the start of Thursday's game as USC jumped out to 21-13 lead after the opening 9:40.
The Trojans maintained at least a two-point lead through the remainder of the first half as USC shot 50 percent (15 of 30).
After Eric Moreland grabbed an offensive rebound and scored to lift Oregon State into a 46-46 tie early in the second half, the Beavers came away empty on their next four possessions and the Trojans got a go-ahead 3-pointer from Nikola Jovanovic and a dunk from Omar Oraby to make it 51-46.
The Trojans led 61-55 with 8:31 remaining when Oraby fouled Angus Brandt, giving him four personal fouls. Oraby then drew a technical foul for arguing the call, earning the 7-foot-2 senior center a fifth personal foul and a disqualification after he had scored 13 points with eight rebounds.
Oregon State took a 68-67 lead on Roberto Nelson's 3-pointer, but Byron Wesley hit two free throws to put the Trojans back in front and then connected from long range to make it 72-68 with 3:05 remaining.
Trailing 72-69, Oregon State's Daniel Gomes missed a dunk attempt in transition, but Hallice Cooke ended up with the loose ball behind the 3-point line and scored to pull the Beavers even with 52.2 seconds left.
The Beavers ended up with the final shot before the end of regulation, but Nelson's pull-up jumper from the left elbow was too strong.