CORVALLIS, Ore. — Until Oregon State's fans descended onto the field in droves, the third-ranked USC Trojans believed they were headed for another victory.

Southern California couldn't find a way to win this close game.

Oregon State capitalized on four turnovers to upset the Trojans, 33-31, yesterday, snapping USC's 27-game Pac-10 winning streak.

USC (6-1, 4-1) had also won 18 straight road games. But the mighty Trojans had shown cracks in their last three games, each a victory by seven points or fewer.

Against the Beavers, they couldn't escape, falling behind early and coming up one play short in the end.

John David Booty's 2-yard TD pass to Steve Smith with 7 seconds left made the score 33-31. But Oregon State's Jeff Van Orsow batted down another pass by Booty on the 2-point conversion to preserve the lead.

"I loved the comeback, but we aren't patting ourselves on the back," coach Pete Carroll said. "We thought we were going to win all the way until we didn't."

Oregon State fans celebrated wildly in the second half when Matt Moore hit Joe Newton with a 9-yard scoring pass and Sammie Stroughter ran a punt back 70 yards for a touchdown to give the Beavers (4-4, 3-2) a 30-10 lead.

USC hadn't lost a regular-season or Pac-10 game since falling, 34-31, to California in three overtimes on Sept. 27, 2003. The Trojans, the 2005 BCS national champions, had won 38 consecutive regular-season games since.