Carroll decides to start Sanchez

USC quarterback Mark Sanchez played late in the game against Oregon last season, mopping up for starter John David Booty in a convincing victory at the Coliseum.

Sanchez’s role will be significantly larger Saturday when he starts for the ninth-ranked Trojans against the fifth-ranked Ducks at Autzen Stadium in Eugene, Ore.

Coach Pete Carroll on Thursday announced Sanchez would start a third consecutive game, noting Booty’s broken right middle finger had not healed enough to ensure accurate passing.

Booty did not throw Thursday after displaying mostly good accuracy and velocity the previous two days.

“He threw the ball well, but there was a few that got away from him and he can’t tell when that was happening,” Carroll said. “That amount of uncertainty was enough to give him another week.

“Hopefully, Mark can make it through the game and we can get a win and we’ll go onto next week and figure it out then.”

For the second time in two weeks, Carroll cut off media access to Sanchez and Booty.

“This has nothing to do with anything other than to help these guys get prepared and keep ‘em quiet and ready for the game,” Carroll said.

Booty had said Wednesday that he was capable of starting but that he did not want to handicap the Trojans by playing at less than full strength.

He will rest his finger until Saturday and will not throw much, “until he has to get warmed up to play, if he does,” Carroll said.

Booty could play if Sanchez were injured or if his performance warranted a substitution, Carroll said. Sanchez’s only pass attempt against Oregon last season was intercepted.

“There’s competition everywhere on this football team and it’s been heightened here at the quarterback spot with this transition and it’s a good thing,” Carroll said.

USC has not replaced a starting quarterback for performance reasons in Carroll’s six-plus seasons. Carroll, former offensive coordinator Norm Chow and then-offensive assistant Steve Sarkisian briefly considered replacing Carson Palmer with Matt Leinart in the 2001 season, but opted to stay with Palmer, who went on to win the Heisman Trophy in 2002.

Sanchez passed for four touchdowns without an interception in USC’s 38-0 win over Notre Dame last week and had one touchdown and two interceptions against Arizona in his debut.

Drew Radovich sat out again because of back soreness, putting redshirt freshman Butch Lewis on track to possibly start at right tackle.

Lewis played most of the last two games at left tackle in place of Sam Baker, who is on track to return against Oregon. “I just go where they tell me to,” Lewis said.

Radovich will rest today with hopes of playing Saturday if his back does not act up on the charter flight to Oregon.

“I don’t know what’s going to happen, maybe build a little hammock in there,” he said.

Radovich said he would take a painkilling shot if necessary and would only sit out Saturday “if I wake up in the morning and my back is locked up. . . . “

Guard Chilo Rachal (knee) continued to work with the first-unit throughout practice and will start against Oregon. . . . Reserve tackle Thomas Herring said he was in a soft cast because of a fractured knee cap.

gary.klein@latimes.com