Ortege Jenkins ran for a pair of TDs and threw for another to lift Arizona over USC.(AP)

Jenkins ran for two scores and hooked up with Bobby Wade on a 75-yard touchdown pass, and Farmer -- a quick, hard-running freshman -- scored on an 80-yard run and finished with 134 yards on 22 carries.

Jenkins' long scoring pass came on the third play of the game and started the Wildcats rolling toward a 21-0 first-quarter lead.

"We wanted to set the tone for the game early," said Jenkins, who ran 1 yard for the Wildcats' second TD and added a 4-yard scoring run in the third quarter. "It has usually been our defense that has done it, but we wanted to this time."

Jenkins passed sparingly after Arizona took its big lead, finishing with six completions in 12 throws, with one interception.

Arizona coach Dick Tomey liked the Wildcats' fast start, but worried a bit afterward.

"I thought we flattened out in the second quarter, but our defense still played well. It looked sometimes that they were going to get back in the game, but that just never happened," Tomey said.

Arizona defensive end Idris Haroon, who had one sack and recovered a fumble, said, "We are attacking offenses. We just want to bury them, put them in the dirt."

USC's Carson Palmer threw three interceptions - two made by Michael Jolivette - and lost a fumble. Palmer was 26-of-50 for 321 yards.

The Trojans also missed two field goals and had both their PAT kicks blocked.

Many in the Coliseum crowd of 49,342 booed as USC lost to an underdog for the second week in a row. The Trojans were ranked eighth nationally before a 31-21 defeat at Oregon State the previous weekend, their first loss to the Beavers in 33 years.

"There is not a whole lot to say," Trojans coach Paul Hackett said. "It was the same scenario. We just didn't come out in the first quarter and play the kind of football that we need to play.

"It's not complicated. We just need to play better. At this point in the season, there is no excuse for it."

The Trojans' scoring came on a 1-yard run by Petros Papadakis in the second quarter, a 27-yard field goal by John Wall in the third, and a 7-yard pass from Palmer to Matt Nickels with 29 seconds left in the game.

Wall took the kicks for USC after David Newbury missed two field goals and had a PAT try blocked in the first half.

On Arizona's long touchdown play that stunned the Trojans early in the game, Wade got a step behind cornerback Kris Richard, caught the ball in stride and sprinted the final 30 yards to the end zone. It was the longest completion of Jenkins' career, and also Wade's longest reception.

Jenkins gave the Wildcats a 14-0 lead when, on fourth-and-goal at the USC 1, he faked a handoff to the right and sprinted left, going untouched into the end zone with 6:59 left in the opening quarter.

Farmer, a 6-foot, 224-pounder, widened Arizona's lead to 21-0 when he took a handoff and started to his left, cut back off tackle and, slicing between a wall of blocks by the Wildcats' offensive left side, broke into the secondary and easily outran the USC defenders.

Jenkins' second scoring run, out of the shotgun, made it 28-9 with 5:10 left in the third quarter, and Sean Keel added a 29-yard field goal for Arizona in the final quarter.

USC was without leading receiver Kareem Kelly, who is out with a leg injury. The Trojans also lost wide receiver Marcell Allmond to a broken shin bone during the game. He is expected to be sidelined for three months.

Palmer was 26-of-50 for 321 yards.