CORVALLIS, Ore. (AP) -- 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 on Saturday, snapping USC's 27-game Pac-10 winning streak and breaking the national championship race wide open.
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 less.
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."
USC started the day as was one of seven unbeaten teams in the country. Now there are six.
Ohio State and Michigan won their games and will hold on to the top two spots in the Bowl Championship Series standings when they come out Sunday. That valuable spot behind the Big Ten powers, previously held by USC, is now up for grabs. All those teams with one loss are feeling a lot better about their chances to play for a national title. And Thursday's Big East battle of unbeatens between West Virginia and Louisville just got a little bigger.
Carroll insisted the Trojans should not be counted out yet.
"You never know. To think that would be a mistake," he said. "It just gets harder. It depends on how we'll finish so we'll see what happens."
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 (5-3, 3-2) a 30-10 lead.
USC, which was coming off an open week that allowed All-American Dwayne Jarrett and fellow receiver Smith to heal injuries, came back with Booty's 4-yard scoring pass to Fred Davis to close out the third quarter.
Booty then found Smith in the end zone and Chauncey Washington ran in the 2-point conversion to narrow it to 33-25 with 12:09 left in the fourth.
After Alexis Serna's 47-yard field goal attempt went wide left, USC got one more shot and it wasn't enough.
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 had won 38 consecutive regular-season games since, but most of those were with Matt Leinart, Reggie Bush and LenDale White in the backfield.
"We've got guys who know how to win," Booty said. "We've won a lot of games. We've won up until now. I don't think anyone's worried or down or anything."
Booty completed 24 of 39 passes for 406 yards and three touchdowns with one interception. Smith caught 11 passes for 258 yards.
Moore completed 21 of 32 passes for 262 yards and a touchdown, while Stroughter caught eight passes for 127 yards.
Beavers fans lingered well after the game, some sitting on the field, not willing to leave after one of the biggest upsets in Oregon State history.
Coach Mike Riley shouted to boosters: "How 'bout those Beavers!" wearing one of the broadest smiles he's ever shown in Corvallis.
Moore, who was booed at Reser stadium by Beavers fans during a loss to Washington State three weeks ago, was cheered this time around.
"I'm so stoked right now, I can't explain it," he said.
Turnovers helped the Beavers take control.
Moore's 22-yard completion Stroughter on Oregon State's first drive set up the quarterback's 1-yard score for a 7-0 lead.
On USC's first possession, Booty's pass intended for Jarrett in the end zone bounced into the arms of Oregon State free safety Bryan Payton, who returned it to the USC 48.
Oregon State didn't get any points out of the drive, but it ended up as a sign of things to come.
Washington ran for a 2-yard touchdown with 10:47 left in the first half to even it at 7 for USC.
Serna kicked three more field goals, two after USC turnovers, in the first half, including a 53-yarder.
Mario Danelo kicked a 29-yard field goal for USC to make it to 16-10 at halftime.
Then Oregon State scored 17 straight, making it 33-10 on Serna's 20-yarder.
"We're not a bad team" USC defensive end Lawrence Jackson said. "We've lost in the past. Unfortunately, we didn't get out of this one with a win."
The Beavers were without tailback Yvenson Bernard, who sprained his right ankle in Oregon State's 17-10 victory over Arizona last weekend. Clinton Polk took his place and had 22 carries for 100 yards.
The last time the Trojans visited Corvallis, it was 2004 and so foggy that it was difficult to see Reggie Bush's wily 65-yard punt return. The Trojans emerged with a 28-20 victory.
Oregon State last defeated the Trojans in 2000. Probably the Beavers' most notable victory over USC came in 1967, when the so-called Giant Killers downed the O.J. Simpson-led Trojans 3-0 on a muddy field in Corvallis.
Thirty-nine years later, the Beavers pulled off another stunner. It was the highest-ranked opponent the Beavers had defeated since their win in 1967, when the Trojans were No. 1.
"I think we were ready for them. I don't think we were in awe of them, but obviously we respected them. They are a very good team," Newton said. "They had, who knows how many Pac-10 wins? We definitely respected them, but we knew we could play with them."