CORVALLIS, Ore - Turns out Southern California was vulnerable. Oregon State capitalized on four USC turnovers to upset Number-three U-S-C 33-31, to snap the Trojans' 27-game Pac-10 winning streak and break the national championship race wide open today. USC had also won 18 straight road games. But the Trojans had shown cracks in their last three games, each a victory by seven points or less. Against the Beavers, they couldn't escape and came up one play short. John David Booty's 2-yard scoring pass to Steve Smith with 7 seconds left made the score 33-31. But Oregon State's Jeff Van Orsow batted down a pass on the 2-point conversion play to preserve the lead. USC started the day as one of seven unbeaten teams in the country. Now there are six. Oregon State fans celebrated wildly in the second half when quarterback 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 a 30-10 lead.