Pe'Shon Howard had a chance to pull USC even after making the first of two free throws with 0.9 seconds left in OT, but missed the second and Devon Collier grabbed the rebound for Oregon State.
"I can't believe we won that game," said Beavers Coach Craig Robinson. "We have been on the other end of so many of those."
Oregon State is now 12-8, (4-4 Pac-12). The next three games are likely to define their season, they now play the Pac-12's top three teams.
Angus Brandt finished with 14 points and Eric Moreland grabbed 10 rebounds and blocked four shots for the Beavers (12-8, 3-4 Pac-12), who trailed, 39-36, at halftime.
Roberto Nelson scored 14 of his 24 points after halftime.
The wild finish saw USC's Byron Wesley miss a layup attempt to tie for USC with eight seconds left and Daniel Gomis rebounded for Oregon State. Gomis passed ahead to Nelson, but Howard stole the ball and was fouled by Gomis driving to the basket. Howard's second free throw off the back of the rim left him 7-8 from the line for the night.
Oregon State's defense was again less than salty at the star, as USC jumped out to 21-13 lead midway through the first half. The Trojans maintained at least a two-point lead through the remainder of the way untul the halftime break.
But OSU cranked things up in the second half and in overtime, with a number of stops -- and the Beavs did it mostly by out-hustling their opponent.
Trailing 72-69 in regulation, Eric Moreland found Hallice Cooke behind the 3-point line, who drilled it to pull the Beavers even with 52.2 seconds left.