LOS ANGELES — USC finally has determined its quarterback pecking order for Saturday's season opener at Virginia, and it has a distinct orange tint to it.

Coach Pete Carroll officially designated Mark Sanchez as the starter Wednesday, a day after doctors checked out Sanchez's left knee and cleared him to play.

Aaron Corp would be the first quarterback off the bench if Sanchez needed relief.

Corp has nudged ahead of Mitch Mustain after a tight camp-long battle.

"There's a little sense of accomplishment," Corp said. "Knowing the coaches have confidence in me gives me confidence in myself."

Carroll described the difference between Corp and Mustain as "negligible" and said Corp got the nod because he's more comfortable with the offensive system.

"It looks like there's a little bit of an edge right now, and that's all there is to it," Carroll said.

Carroll has said repeatedly that the Corp-Mustain competition will continue indefinitely. Mustain is embracing the possibilities.

"There's a long time to go, it's a long season," Mustain said. "We'll see what happens. I'm not down about it."

Neither Corp nor Mustain is as far along as Sanchez, and playing either backup would require the coaches to simplify the game plan.

VIRGINIA'S 3-4

USC's offense will see something a little unusual when it steps on the field at Virginia: a 3-4 defense.

The 3-4 is less popular than the 4-3, and USC won't face another one until the Cal game Nov. 8.

The biggest difference is the way the defensive linemen attack: They go head-up on the offensive linemen, trying to clear space for the linebackers to make tackles.

"They teach it really well," USC offensive line coach Pat Ruel said of the Cavaliers. "It presents problems because not many teams run a 3-4."

Ruel said 3-4 defenses can be difficult against offenses like USC's that use zone blocking. Virginia allowed just 2.9 yards per rush last season.

The threat of blitzes is another concern, especially considering USC's inexperience up front, where left guard Jeff Byers is the only full-time returning starter.

But Byers believes the barrage of blitzes the line faced during training camp has the group prepared.

"The only way you teach offensive linemen to pick up blitzes and see blitzes is to get beat by blitzes. And we've obviously been beaten a fair share of times this camp," Byers said. "I really feel like we're ready for any kind of blitz situation they throw against us."