Marcio Jose Sanchez / AP

Stanford linebacker Trent Murphy, left, sacks USC quarterback Matt Barkley on Saturday night. It was one of four sacks by the Cardinal in the 21-14 upset of the No. 2 Trojans.

updated 4:04 a.m. ET Sept. 16, 2012

STANFORD, Calif. - David Shaw tried to hold back his emotions on the sideline. The second-year Stanford coach watched his players bounce on both sides of him, then fans swarm the field from all angles, and he finally couldn't resist flashing a giant I-told-you-so smile anymore.

No Jim Harbaugh and no Andrew Luck, but the Cardinal still have every answer for Matt Barkley and Southern California.

Josh Nunes threw a go-ahead 37-yard touchdown to Zach Ertz, Stepfan Taylor ran for 153 yards and scored two touchdowns, and No. 21 Stanford upset second-ranked USC 21-14 on Saturday night for its fourth straight win in this series.

"We don't want to be that team known for one victory," Shaw said. "We want to be known for victory after victory, stacking wins on top of wins."

Make it four-of-a-kind against that long-time powerhouse from down south.

Heisman Trophy hopeful Matt Barkley threw for 254 yards and two interceptions while completing only 20 of 41 passes. He was sacked twice on the final drive for the Trojans (2-1, 0-1 Pac-12) and threw out of bounds on a final, desperate heave on fourth-and-39 from USC's 25-yard line.

Coming out of a two-year bowl ban, USC had national title hopes this season. Now the Trojans, who were held scoreless for the final 41:19, will have to climb out of another hole to get there.

"You learn and go back to playing Trojan football," said a disappointed Barkley, who has beaten every conference teams but is 0-4 against Stanford. "We got to just not put the blame on anybody, learn from our mistakes and make sure we bounce back."

Once the clock hit zeros, a sold-out crowd of 50,360 at Stanford Stadium rushed the field, tossing streamers and jumping in a wild celebration at midfield with Shaw and Stanford players caught in the middle of the mess. Stanford (3-0, 1-0) is 3-0 for the third straight season for the first time since 1970-72 and has its longest winning streak ever against USC in a rivalry that dates back to 1905.

Jim Rogash / Getty Images The Week in Sports Pictures The nation grieved for those hurt, killed and affected by the Boston Marathon bombings. After one of the suspects was caught on Friday — following a day-long lockdown and manhunt — sports returned to Boston over the weekend.

"I love the energy and I love the enthusiasm," Shaw said. "But we are not surprised."

He might be the only one.

Luck, the No. 1 overall pick by the Indianapolis Colts, two-time Heisman Trophy runner-up and perhaps the greatest player in school history, is gone and so much about this season seemed uncertain. Now the only chance another senior quarterback and possible No. 1 overall pick has for revenge against the Cardinal now is a rematch in the Pac-12 title game.

"It's not the end of the world," said USC coach Lane Kiffin said, now 0-3 against Stanford. "We'll get back on the plane, go home and we'll get better."

Stanford's Jordan Williamson missed field goals of 47 and 23 yards and had a 51-yarder blocked by T.J. McDonald. With a defense that flustered Barkley and a new quarterback that found his footing late, the kicker who missed three field goals in the Fiesta Bowl loss to Oklahoma state last season could smile in the pile with everybody else.

Except for the Trojans, that is.

A year after Luck led Stanford back in a 56-48 triple-overtime thriller at the Coliseum, a new crop of Cardinal players delivered another moment to savor.

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