USC got 142 yards rushing and a touchdown from Joe McKnight . Matt Barkley completed 21 of 31 passes for 196 yards and a touchdown but had three passes intercepted and fumbled once. Stanford scored touchdowns after each of the turnovers.

Andrew Luck was as impressive passing as Gerhart was running. He completed 12 of 22 passes for 144 yards and two touchdowns. He also rushed for 61 yards and a touchdown.

Stanford, which rushed for 325 yards and averaged 6.5 yards a carry, has now delivered USC's lost three losses at home -- in 2001, 2007 and 2009.

Cardinal tailback Toby Gerhart , who USC didn't think was fast enough to recruit as a tailback, rushed for 178 yards and three touchdowns. He also ran for more than 100 yards last season against the Trojans.

USC simply had no answer for a Stanford offense that scored 51 points against Oregon last week.

USC fell to 7-3 overall and 4-3 in the Pac-10 -- the first time the Trojans have lost three games in a season since 2001, Carroll's first year as coach.

Not a good day for defensive guru Pete Carroll , who was clearly hot when he met Stanford Coach Jim Harbaugh on the field after the game. Carroll gave his rival a terse "good game," but he didn't like Stanford going for a two-point conversion late in the game, already up 48-21.

In a key 55-21 Pacific 10 Conference win over the Trojans today at the Coliseum, the Cardinal scored more points against USC than any team in history.

But not the good kind.

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Stanford 55, USC 21 (late in fourth quarter)

Another Matt Barkley interception, another Stanford touchdown.

The USC freshman has four turnovers, and Stanford has converted each of them into a touchdown.

Tyler Gaffney just made it a record-setting day at the Coliseum, putting up more points against the Trojans than any team in history.

To cap it off, the television telecast showed Stanford's Richard Sherman and Ekom Udofia on the sideline taunting USC by giving the "V" sign and saying, "Fight on, USC, fight on."

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Stanford 48, USC 21 (6:47 remaining in game)

The rout is on.

USC has no answer for Stanford's offense.

Toby Gerhart's six-yard touchdown run put the Cardinal within range of scoring 50 points.

At least USC came up with a defensive play to thwart that -- Stanford's Stepfan Taylor was stuffed on a two-point conversion run, saving the Trojans a (very) little embarrassment.

Gerhart has rushed for 178 yards and three touchdowns in 29 carries.

So much for a happy homecoming for the Trojans.

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Stanford 42, USC 21 (early fourth quarter)

Matt Barkley is having a good day in that few of his passes are hitting the ground.

Most have gone to Trojans receivers.

But two now haven't.

Stanford's Richard Sherman's interception of a Barkley out pattern has put Stanford up by three touchdowns.

Sherman made the pick in full stride and raced 43 yards untouched for the score.

Barkley has completed 21 of 30 passes for 196 yards and a touchdown with the two interceptions.

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Stanford 35, USC 21 (early fourth quarter)

Remember all the eye rolls when Stanford Coach Jim Harbaugh said Andrew Luck was the best quarterback in the nation?

Doesn't seem so crazy watching him this afternoon.

Every time USC puts together some plays to crawl back into the game, Luck has an answer.

His 24-yard touchdown pass to tight end Coby Fleener has put Stanford back up by two touchdowns.

It was an impressive pass and reception -- Luck firing a line drive and the 6-foot-6, 250-pound Fleener making a great catch and then holding on after a big hit from Taylor Mays.

-- Mike Hiserman

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Stanford 28, USC 21 (end of third quarter)

USC quarterback Matt Barkley completed third-down passes of 17 yards to Joe McKnight and 19 yards to Brice Butler during an eight-play, 76-yard scoring drive that kept the Trojans in the game.

Barkley also had a key block on a 17-yard cutback run by McKnight.

McKnight did it alone on a 28-yard touchdown run that kept the Trojans within seven points.

McKnight has rushed for 132 yards and a touchdown in 13 carries. Barkley is 20 of 26 for 189 yards and a touchdown, with an interception and a fumble.

USC has gained 308 yards, Stanford 306.

Stanford's Toby Gerhart has run for 119 yards in 23 carries.

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Stanford 28, USC 14 (third quarter)

USC Coach Pete Carroll was concerned about the running ability of Stanford quarterback Andrew Luck.

With good reason.

Luck scrarmbled for 19 yards on one play of a 68-yard scoring drive that he capped with a six-yard run for a touchdown after a nifty fake to Toby Gerhart.

Luck has rushed for 45 yards and a touchdown in five carries. He has completed 10 of 19 for 107 yards and a touchdown.

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Stanford 21, USC 14 (early in third quarter)

The momentum has shifted. But will it be enough?

USC linebacker Chris Galippo forced Stanford tailback Toby Gerhart to fumble with 11:23 left in third quarter and safety Taylor Mays recovered the ball at the Cardinal 36-yard line.

On the first play of the ensuing possession, Matt Barkley threw a 36-yard touchdown pass to Brice Butler to pull the Trojans to within seven points.

Barkley has completed 16 of 21 passes for 152 yards and a touchdown, with an interception. Butler has four catches for 77 yards.

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Stanford 21, USC 7 (halftime)

USC better figure out a way to slow down Stanford's offense or it's going to be a long day at the Coliseum.

Andrew Luck has completed six of 19 passes for 91 yards and a touchdown and running back Toby Gerhart has run for 73 yards and two touchdowns in 14 carries.

USC quarterback Matt Barkley seemed to find some rhythm on the Trojans' final drive, but it was all for naught.

USC had the ball at its 13 with 2:20 left and moved down the field on five consecutive completions by Barkley. But on first and 10 at midfield, the Trojans were penalized for holding. Barkley was sacked on third and one and his fourth down pass fell incomplete.

Barkley is 13 of 17 for 107 yards, but his fumble and an intercepted pass led to Cardinal touchdowns. USC tailback Joe McKnight has rushed for 82 yards in eight carries.

Stanford has outgained USC, 206-182.

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Stanford 21, USC 7

Stanford's offense has the Trojans reeling.

Andrew Luck's 22-yard pass to fullback Owen Marecic moved the Cardinal into USC territory where running backs Toby Gerhart and Stepfan Taylor went to work.

Luck's 15-yard pass to receiver Ryan Whalen gave the Cardinal a first down at the Trojans' three. Stanford then went to a no-huddle, catching the Trojans off guard.

USC tried to hurry in players, but it was too late to stop Gerhart's three-yard touchdown run. The Trojans were called for illegal substitution and offsides on the play.

Gerhart has run for 65 yards and two touchdowns in 12 carries.

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Stanford 14, USC 7

The Trojans show some life.

Joe McKnight's 51-yard run started a nine-play, 80-yard drive that culminated with Allen Bradford's two-yard touchdown run.

McKnight has gained 85 yards in seven carries. Matt Barkley has completed five of seven passes for 46 yards.

Barkley's pass to receiver Travon Patterson on a third-and-five at the 24 kept alive the drive.

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Stanford 14, USC 0 (end of first quarter)

Andrew Luck has completed six of 10 passes for 46 yards and a touchdown and Toby Gerhart has rushed for 43 yards and a touchdown in eight carries.

But USC quarterback Matt Barkley lost a fumble and had a pass intercepted to set the table for the Cardinal.

Trojans tailback Joe McKnight broke off a 51-yard run with just under 1:30 left in the quarter, and the Trojans enter the second period with a first down at the Stanford 18.

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Stanford 14, USC 0

Matt Barkley continues to struggle.

Stanford defensive end Matthew Masifilo intercepted Barkley's short pass intended for tailback Joe McKnight with 4:04 left in the first quarter.

The Cardinal took over at USC's 35, and Toby Gerhart's 17-yard run on a third-and-nine helped set up his one-yard touchdown run.

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Stanford 7, USC 0

The Cardinal took advantage of a USC turnover to take the early lead on Andrew Luck's five-yard touchdown pass to fullback Owen Marecic.

USC had forced Stanford to go three and out on the game's first possession. The Trojans looked to have their offense in sync as they drove from their 33-yard line to the Cardinal 17 in four plays, including a 19-yard pass from Matt Barkley to Ronald Johnson.

But on first down, Stanford linebacker Will Powers stripped the ball from Barkley and linebacker Clinton Snyder recovered the fumble.

Luck then drove the Cardinal 71 yards in 12 plays for the 7-0 lead.

-- Gary Klein

Photo: Stanford running back Toby Gerhart leaps over USC's Will Harris during the first half Saturday. Credit: Gina Ferazzi / Los Angeles Times