In the fourth quarter, LaMichael James burst through the Trojans’ defensive line for 10 yards and another first down. Only this time, he fumbled as he was tackled to the ground and USC redshirt senior safety Will Harris recovered the ball, returning it 66 yards for a touchdown.

At least, that’s what it looked like. After reviewing the play, officials overturned the fumble, ruling that James’ knee was down before he lost control of the ball.

Running wild · Oregon quarterback Jeremiah Masoli torched the Trojan defense on the ground, rushing for 164 yards and one touchdown. - Dieuwertje Kast | Daily Trojan

It was that kind of night for the No. 5 Trojans, who suffered their worst loss since a 27-0 shutout against Washington in 1997. James ran for 184 yards and one touchdown and junior quarterback Jeremiah Masoli piled on 386 yards of total offense as the Ducks rolled to a 47-20 triumph over USC (6-2, 3-2 Pac-10).

Oregon fans, clad in black and dark green, rushed the field after the final whistle sounded on the Trojans’ second loss at Autzen Stadium in three years. The Ducks (7-1, 5-0) had previously defeated USC 24-17 in 2007.

“We just got beat up upfront,” USC senior safety Taylor Mays said. “We didn’t tackle well, and they busted us. They hit us in the mouth, and they kept hitting us in the mouth.”

For the third straight year, the Trojans watched their national title hopes melt away in the Oregon rain. Last season, they fell to Oregon State, 11 months after their previous ill-fated visit to Eugene, Ore.

But neither of those games was decided by more than a touchdown. In fact, the Trojans had not lost by more than seven points since a 27-16 loss to Notre Dame in 2001.

This proved to be a much more lopsided defeat, as Oregon’s 47 points were the most allowed by any USC squad since UCLA scored 58 in 1996. The Ducks’ 613 yards on offense — 391 of those came on the ground — were second only to the 623 Notre Dame racked up against the Trojans in 1946.

“We’ve never been in something like that,” said USC coach Pete Carroll. “They did everything they wanted to do. It was really pretty easy for them.”

This latest loss puts the Trojans’ streaks of seven consecutive Pac-10 titles and seven straight BCS appearances in serious jeopardy. Meanwhile, the Ducks, undefeated in Pac-10 play, look primed to take their first conference crown since 2001.

Masoli, who passed for 222 yards and ran for another 164 on his way to two scores, put the Ducks up 10-3 on a 3-yard run late in the first quarter. Minutes later, USC freshman quarterback Matt Barkley threw a three-yard strike to USC junior wide receiver Ronald Johnson to tie the game.

Barkley, who completed 21 of 38 throws for 187 yards with two touchdowns and an interception, directed several efficient drives to keep it close in the first half. But the Trojans’ defense would never find a way to slow down the Ducks, who led 24-17 at halftime.

James was especially difficult to stop, running all over the field in a performance that may have reminded USC fans of Oregon State’s Jacquizz Rodgers. Another diminutive running back, Rodgers gave the Trojans fits in the Beavers’ upset win last year and also accounted for 169 yards of offense a week ago at the Coliseum.

“We had trouble tackling him,” Carroll said of James. “We had him stopped in the backfield three, four, five times, and he spun around, ducked around and got out and made some big plays.”

Over the next two quarters, USC struggled to get anything going while James and Masoli continued to carve up the Trojans’ defense.

With 5:50 left in the third quarter, James took the ball into the end zone from five yards out to increase the lead to 14. Fellow redshirt freshman defensive back Kenjon Barner scored on a 3-yard run to make it 41-20 at the end of the quarter.

On defense, the Ducks shut down the Trojan attack. After gaining 193 yards and finding the end zone twice in the first half, USC could only manage a single field goal over the final 30 minutes.

It was certainly a new experience for the Trojans, but mostly it was just downright bewildering.

“I can’t even believe it right now,” said junior running back Joe McKnight. “I didn’t lose like this in high school, and I haven’t lost like this [in college]. Just to have that feeling for the first time — I hate it.”