USC had been embarrassed at home by Stanford before, but not like this.

Not in November. Not on homecoming. And certainly not by 34 points.

But behind the power running of senior running back Toby Gerhart, the No. 25 Cardinal (7-3) did, thoroughly overpowering the No. 11 Trojans, 55-21, in a shocker before 90,071 celebrating homecoming at the Coliseum. Stanford’s 55 points were the most ever scored against USC.

Daily Trojan | Mannat Saini

“This feels really weird,” USC coach Pete Carroll said after the game.

It looked like things would go the Trojans’ way when they forced a three-and-out on Stanford’s first drive and immediately drove inside the Cardinal 20.

But freshman quarterback Matt Barkley fumbled a first-down snap under duress from the Stanford defensive line. From there, it was all Cardinal in the first quarter, as redshirt freshman quarterback Andrew Luck threw for one touchdown and Gerhart ran for another.

“We started really fast,” Luck said. “We knew it would be a tough game, but starting fast really helped.”

Gerhart consistently busted through the USC front seven, totaling 29 rushes for 178 yards and three touchdowns. He ran for nine first downs.

“We’ve seen him run the ball like that week in and week out, so we’ve just gotta tackle him,” junior linebacker Malcolm Smith said. “But he just got out.”

Opponents all season have mentioned Stanford’s physicality, especially when running the ball. The Cardinal overpowered Oregon a week ago with 254 yards on the ground. This time, they had 325.

“That’s something that we have to do as a team: be physical and play physical,” Stanford coach Jim Harbaugh said in his postgame press conference. “And we do other stuff offensively that compliments the physical side.”

Luck, Harbaugh’s 19-year-old signal-caller and admitted protégé, outplayed his freshman counterpart Barkley, completing 12-of-22 passes for 144 yards and two touchdowns to Barkley’s 21-of-31 for 196 yards and a touchdown. The biggest difference was Barkley’s three interceptions — all three of which resulted in Stanford touchdowns.

Barkley said after the game that he probably shouldn’t have thrown at least one of them. The picks served to stymie USC’s running game, which was mostly effective.

Junior running back Joe McKnight carried the ball 16 times for 142 yards and a touchdown, but the Trojans again failed to convert a total of eight third and fourth-down opportunities.

“One of the big things was to be able to stop the running game,” Harbaugh said. “We didn’t stop it, USC popped some runs, but for the most part it wasn’t 10, 10, 10. We got some stops and some sacks.”

USC had fostered some momentum after a Taylor Mays fumble recovery gave the Trojans the ball on the Cardinal 36, down 21-7 in the third quarter.

Barkley then delivered a 36-yard touchdown strike to redshirt freshman receiver Brice Butler to make the score 21-14.

But Stanford would answer back with a methodical 10-play drive capped off by a 6-yard touchdown run by Luck.

“That was a big momentum shift, and when I caught it I was like ‘Let’s go,’ now that we’d scored,” said Butler, making his first career start in place of the injured Damian Williams. “The whole team was feeling that way.

“Then, it kinda died down.”

USC would score once more, but Stanford again responded quickly. The Cardinal’s last five drives all ended in touchdowns.

With the 34-point loss, USC has been outscored 174-131 in its last five games.

This is also the first time since Carroll’s first year, 2001, that the Trojans have lost three games in one season.

“Things are looking nasty right now,” Smith said.

USC’s last three home losses have all been against Stanford, but the Trojans said that didn’t matter.

“Any team that beats us, they’re surprised,” Butler said. “They didn’t think it was gonna happen.”

Stanford’s Gerhart, a member of the 2007 team that upset the Trojans 24-23 at the Coliseum, agreed to a certain extent.

“I was surprised a little bit,” Gerhart said. “They’re USC and have been the premier Pac-10 team.

“We’ve been the underdogs.”

But while Stanford stays in the thick of the Pac-10 championship race, the Trojans are essentially eliminated from BCS bowl and Pac-10 title contention. They must now face the likelihood of a pre-New Year’s bowl game.

But for now, the Trojans have a bye-week break before crosstown rival UCLA comes to town on Nov. 28.

“If you think about it, it probably comes at the perfect time,” Butler said. “We lost, and now we have to sit here and think about it for two weeks.”