BERKELEY, Calif. — Taylor Mays and a dominating Southern California defense overshadowed any offensive deficiencies for the Trojans and overwhelmed Jahvid Best and the California offense.

Mays set the tone with an interception on the first drive of the game, Damian Williams returned a punt for a touchdown and the seventh-ranked Trojans beat No. 24 California 30-3 Saturday night.

Joe McKnight ran for 119 yards and scored the only two offensive touchdowns for USC (4-1, 2-1 Pac-10) with a 38-yard run on the first drive and a 5-yard run late in the fourth quarter that emptied the stadium.

Jordan Congdon kicked three field goals and the defense did the rest, holding Best to 47 yards on 14 carries and keeping the Golden Bears scoreless until Vince D'Amato's 29-yard field goal with 10:45 remaining.

The win capped an emotional week for the Trojans. Running back Stafon Johnson is still recovering from seven hours of reconstructive surgery Monday after a weight bar fell on his neck, crushing his larynx and throat. With Johnson watching from his hospital room, his teammates delivered against Cal.

After losing 16-13 two weeks ago at Washington, USC didn't give up a score until 22 seconds remained in last week's 27-6 victory against Washington State and then blanked Cal until early in the fourth quarter.

With the defense playing this well, the Trojans are making it easy on freshman quarterback Matt Barkley. Barkley was inconsistent in this game, completing 20 of 35 passes for 283 yards and an interception. He moved the ball down the field with ease but struggled to punch the ball into the end zone.

It didn't matter with the way the Trojans' defense played. They had the answer for whatever trick Cal coach Jeff Tedford tried. Best took a handful of direct snaps in Cal's version of the wildcat, the Bears went for it twice on fourth down, and even a well-designed trick play didn't work.

In the third quarter, Cal came out of a timeout with Shane Vereen standing next to its sideline, just on the field of play. With no defender near him, Vereen went out for a pass, but instead of a big play, Kevin Riley threw high for an incompletion. The next play was a screen pass that left tackle Mike Tepper caught for an illegal touch penalty.

That was the kind of day it was for Riley, who was 15 for 40 for 199 yards and an interception in his second straight sub-par performance. He was just 12 for 31 for 123 yards in last week's 42-3 loss at Oregon.

Riley's interception in the end zone on the opening drive was his first of the year. Six plays later, McKnight dived into the end zone at the end of his long run. Williams' 66-yard punt return made it 17-0 in the second quarter and the rout was on. Williams caught eight passes for 101 yards.

After scoring 146 points in its first three games, Cal has just six the past two weeks. Cal has failed to score a touchdown just three times in eight years under Tedford, with two of them coming the past two weeks. The other was against USC in 2007, which was the last time Cal lost at home before Saturday night.

Even the speedy Best couldn't get going against the Trojans. On one play in the first half, he was chased down by Mays for no gain on a third-and-2 run.