PALO ALTO — — This time it had nothing to do with Luck.
Not a quarterback by that name or a series of unexplainable events.
As USC Coach Lane Kiffin and his second-ranked team dejectedly walked off the field at Stanford Stadium on Saturday night, they could blame only themselves for a 21-14 upset loss to the Cardinal.
With or without Andrew Luck, the No. 1 pick in the NFL draft, No. 21 Stanford showed once again that it knows how to beat the Trojans.
Junior quarterback Josh Nunes, starting only his third game, showed Luck-like pluckiness during the fourth quarter and led Stanford to its fourth consecutive victory over USC, a Cardinal feat unprecedented in a series that dates to 1905.
USC, held scoreless in the second half, fell to 2-1 overall and 0-1 in the Pac-12 Conference.
"We kind of got basically humbled today," linebacker Hayes Pullard said.
Just as they did in conference openers on the road in 2008 at Oregon State, 2009 at Washington and last season at Arizona State, the Trojans stumbled.
And the recipe was much the same.
The Trojans committed three turnovers, including interceptions on two consecutive passes by quarterback Matt Barkley, who looked nothing like the Heisman front-runner.
Barkley was sacked four times and was under pressure throughout the game. He completed only 20 of 41 passes for 254 yards and did not throw a touchdown pass.
Asked if this was his toughest loss, Barkley said, "Yeah, it hurts."
Stanford neutralized receivers Marqise Lee and Robert Woods and limited the Trojans to 26 yards rushing.
"We were a little out of sync," tight end Xavier Grimble said. "That's a tough defense, a veteran defense that has been together."
Nunes, the former Upland High standout, completed 15 of 32 passes for 215 yards and two touchdowns, with two interceptions.
And he was at his best when it counted most, engineering two fourth-quarter scoring drives for to improve Stanford to 3-0.
According to USC tight end Randall Telfer, the Trojans were "not as mentally prepared as we should have been."
The Trojans led, 14-7, at halftime and had a chance to extend the lead when they drove to Stanford's 13-yard line. But the absence of kicker Andre Heidari came back to haunt them.
On fourth down, Kiffin sent in kicker Alex Wood, but the freshman walk-on lined up in the backfield next to Barkley, who took a snap and threw a pass to fullback Soma Vainuku in the end zone. But nickel back Ronnie Harris broke up the play.
The teams traded possessions before Nunes hit tight end Zach Ertz for a 24-yard gain that set up the tying touchdown. On first and 15 at the Trojans' 23, Taylor took a short pass in the right flat and slipped four tackles en route to the end zone with 10 seconds left in the third quarter.
The Trojans went three and out on the ensuing possession, setting the stage for Stanford's upset.
Nunes took over at the Stanford 21 and moved the Cardinal downfield. On third and 10 at midfield, he scrambled for 12 yards to pick up a first down, looking much like the agile Luck did in his three victories over the Trojans.
On second down at the 37, he dropped back and hit Ertz with a 15-yard strike and Ertz broke two tackles before falling into the end zone for a 21-14 lead.
USC got the ball for a final time with 2:14 left and seemed to get a break when a pass initially ruled incomplete was overturned on review, giving the Trojans a first down and keeping their hopes alive.
But linebacker Trent Murphy sacked Barkley, and after a false- start penalty, linebacker John Flacco sacked Barkley again.
On fourth and 40 from the Trojans' 24, Barkley lofted a long pass to Woods along the right sideline. But the ball fell incomplete and Stanford's victory was secure.
USC led, 14-7 at halftime despite committing turnovers on three consecutive possessions, including interceptions on consecutive passes by Barkley.
Stanford missed an early field goal, and the Trojans wasted their first opportunity before freshman receiver Nelson Agholor caught a pass and then raced 49 yards to the Stanford two.
Harkening to the infamous "Bush Push" touchdown at Notre Dame in 2005, Silas Redd scored with an assist from left tackle Aundrey Walker.
On second and goal from the two, Redd took a handoff and appeared to be stopped. But he kept his feet moving and Walker wrapped him up and appeared to pull him across the goal line.
Stanford wasted little time responding.
Stepfan Taylor took a handoff from Nunes, broke off right tackle and then sidestepped one tackler and slipped another before breaking toward the left sideline and outrunning the Trojans for a 59-yard touchdown.
USC went ahead early in the second quarter with a 14-play, 58-yard drive highlighted by two fourth-down completions by Barkley.
Barkley connected with tight end Randall Telfer for eight yards on a fourth-and-three pass. Woods gained 24 yards on a fourth-and-19 play from the 25-yard line.
Redd scored his second touchdown on a one-yard run for a 14-7 lead with 11:19 left in the second quarter.
But that was all the Trojans would score, as Nunes and the Cardinal did it to them again.