LOS ANGELES — Toby Gerhart rushed for 178 yards and three touchdowns and No. 25 Stanford emphatically followed up its 2007 upset at the Coliseum by beating No. 11 Southern California today, 55-21, the most points ever allowed by the Trojans.

The loss was the Trojans' worst since a 51-0 defeat at home against Notre Dame in 1966 and essentially ended USC's seven-year run as Pac-10 champions.

Andrew Luck threw two touchdown passes and ran for another score for the Cardinal (7-3, 6-2 Pac-10), who followed up their surprising rout of Oregon last week with a strong start and a big finish at the Coliseum, where the Trojans (7-3, 4-3) haven't lost to any other opponent since 2001, going 47-2.

Richard Sherman returned an interception 42 yards for a score with 11:41 to play, part of a 27-point fourth quarter for the Cardinal.

For the second time in three weeks, coach Pete Carroll endured the worst defeat of his nine seasons at USC.

Stanford's 24-23 victory as a 41-point underdog in 2007 was a major shocker, yet this win barely even qualified as an upset — which might be the most incredible thing of all about the Trojans' downward slide.

Luck soundly outplayed fellow freshman quarterback Matt Barkley, while Gerhart steamrolled the once-vaunted USC defense in another huge game for his Heisman Trophy hopes. Stanford piled it on late, scoring four touchdowns in the fourth quarter after leading 28-21 entering the period.

And the Cardinal did it on USC's homecoming, no less, in front of 90,071 awfully quiet fans.

Two weeks after USC's 47-20 loss at Oregon — previously the worst of Carroll's tenure — the Trojans again struggled with an offense that has rarely clicked this season. When Sherman jumped on Barkley's short pass and returned it down the USC sideline to put the Cardinal up 42-21, Coliseum fans headed for the exits with unfamiliar emotions.

Barkley went 21 of 31 for 196 yards with three interceptions in his third straight unimpressive game for the Trojans. Carroll has stuck with the freshman all season, but Barkley made turnovers on USC's first two drives to put the Trojans in an early hole, while Luck scarcely made a mistake.

Joe McKnight rushed for 142 yards and a score for the Trojans, who fell behind 21-7 at halftime without top receiver Damian Williams, who has a sprained ankle. Freshman Brice Butler caught a scoring pass among his six catches for 96 yards, but USC's offense rarely found a rhythm after its first drive ended in a fumble by Barkley deep in Stanford territory.

Although USC kept it close through three quarters, the fourth was a long celebration for the Stanford band, a small cheering section and the players who already are bowl-eligible for the first time since 2001. After Gerhart's third touchdown, Stanford coach Jim Harbaugh even attempted a 2-point conversion, but USC stopped the try at the goal line.

After shaking hands, the Cardinal raised their helmets and raced to the Coliseum corner in front of their cheering section for a raucous celebration.

Few of the Cardinal's key players from that 2007 upset. Tavita Pritchard, the backup quarterback who led that 2007 victory, watched most of this game wearing a headset before playing the final minutes of the blowout.

The 2007 Cardinal couldn't even manage a winning season. These Cardinal still have a shot at the Rose Bowl.