What other explanation can there be?

The Trojans entered Saturday's game as 41-point favorites over a Stanford team coming off three one-sided losses and playing its first road game of the season.

The site was the Los Angeles Coliseum, where USC had won 35 straight since losing to the Cardinal six years ago in the fourth game of the Pete Carroll era.

Oh, one more thing — quarterback T.C. Ostrander couldn't play, meaning Tavita Pritchard would make his first career start against one of the nation's toughest defenses.

Final score: Stanford 24, USC 23. The Cardinal scored the winning points with 49 seconds remaining on Pritchard's 10-yard touchdown pass to Mark Bradford on fourth-and-goal and Derek Belch's conversion.

Four plays earlier, Stanford converted on fourth-and-20 when Pritchard hit Richard Sherman for a first down at the USC 9, just past the first-down marker.

There was fair warning things weren't quite right a week earlier, when then-No. 1 USC was holding on at the end of a 27-24 victory at Washington over a team coming off two straight losses.

After that, the Trojans fell to No. 2 in the AP Top 25, just two points behind LSU. Now, after being victimized by one of the most startling upsets in college football history, USC (4-1, 2-1 Pac-10) is ranked 10th.

"We lost. We've got to face that fact and move on," said Trojans quarterback John Booty, who passed for 364 yards but threw four interceptions, including one that was returned for a touchdown and another that set up the go-ahead touchdown. "Now, we have to put it behind us."

The same might be said for USC's national championship hopes, although with all the upsets happening, it's possible there won't be one unbeaten team standing when the regular season ends, much less two.

"Our season's not over," defensive end Lawrence Jackson said. "This loss is not devastating. We still have seven games left. We are still a good team with great coaches, even though we walked out of here with a loss. We need to find character and bounce back."

That shouldn't be too difficult the next couple of weeks, with Arizona (2-4) paying a visit next Saturday and the Trojans traveling to Notre Dame (1-5) on Oct. 20. Though, after what happened Saturday night, no game is a walkover right now for USC.

After that, USC hits the road of the nastiest part of the schedule with games at No. 2 California, No. 9 Oregon and No. 14 Arizona State.

USC had to face Stanford (2-4, 1-3) without several topflight players sidelined by injuries including tailbacks Stafon Johnson and C.J. Gable, offensive linemen Kristofer O'Dowd and Chilo Rachel, linebacker Brian Cushing and defensive back Josh Pinkard.

Still, the Trojans pride themselves on their talent and depth, understandable considering they've been at or near the top of the recruiting wars under Carroll, who has coached USC to a 69-13 record since taking over.

USC dominated Stanford statistically, rolling up 459 yards of total offense to 235, but committed five turnovers while forcing only one.

The game turned late in the third quarter, after USC had taken a 16-7 lead. Not counting their final possession, when they took a knee with the game in hand, the Cardinal gained 186 yards and scored 17 points the last three times they had the ball.

"Stanford deserves all the credit," Carroll said. "They did a heck of a job and we just had a ton of mistakes. We made enough mistakes and they capitalized. This just goes to show, the guys who play better win."

Booty cracked a bone on the tip of his middle finger on his throwing hand when he hit it on a helmet in the second quarter, but played on.

"He fought through it and was doing all right," Carroll said. "We could have made a change but we went with our guy. I don't know about next week."

USC dropped several passes, committed eight penalties for 80 yards, and made several other mistakes as well.

The young wide receivers continue to struggle, perhaps making Booty appear to be playing worse than he really is, and the offensive line didn't protect well.

Pritchard, a 6-foot-4, 200-pound sophomore from Tacoma, Wash., entered having thrown three passes for the Cardinal. He completed 11 of 30 for 149 yards and the winning touchdown with one interception.

Not great numbers, but good enough.