"He was one of my best friends," Williams said recently. "Not only that, the quarterback is leaving. You didn't quite know who was going to be the next guy. I can't lie and say I didn't think about it."
The Trojans are happy that Williams came back.
The fourth-year junior was USC's most dependable receiver last season, catching a team-high 58 passes for 869 yards and nine touchdowns.
Williams said before the Rose Bowl game against Penn State that he had no intention of leaving for the NFL.
Then came Sanchez's dynamic New Year's Day performance against the Nittany Lions. The junior passed for four touchdowns and ran for another, setting in motion a process that culminated with his decision to pass up his final season of eligibility.
"Mark's process was really grueling for everybody -- I know for him, but even for me," said Williams who caught 10 passes for 162 yards and a touchdown in the Rose Bowl.
"We talked for that whole week, and I'm talking like till 2 o'clock in the morning. . . . It kind of weighed on me just because I felt such a part of the decision."
Williams' decision to return, he said, centered on two factors.
"It came down to I was 14 hours short of graduating, it would have been pointless to leave," he said. "And, I wasn't quite ready."
Coach Pete Carroll agreed.
"He's got to establish himself, and he has a chance to show he's a consistent big-time performer," Carroll said.
Williams, a team captain, was not able to show a lot during training camp. He was sidelined last week because of bruised quadriceps, but expects to return soon, possibly when the Trojans resume practice on Tuesday.
Williams, who transferred from Arkansas in 2007, said he had no preference in regard to who might become the Trojans' starting quarterback.
Williams and third-year sophomore Aaron Corp spent 2007 as redshirts, and they roomed together this month during training camp.
Williams got to know freshman Matt Barkley during spring practice and summer workouts, and his relationship with junior Mitch Mustain dates to when they played youth football together in Arkansas. "All of them are good," Williams said. "Whoever the coaches choose is going to do well."
Shane Horton moved from safety to linebacker early in camp to add depth and to compete for playing time.
On Saturday, he produced the only points in the Trojans' third scrimmage by tackling tailback Curtis O'Neal in the end zone for a safety.
Of his move to linebacker, the 6-foot-1, 215-pound Horton said: "I think it fits my style a little more. It's cool because it brings out a little more of the competitor in me.
"I can talk a little more smack. Get the juices flowing a little bit. . . . It feels like you're involved in every play."
Cornerback Shareece Wright is looking forward to returning to practice after having fluid drained from his right knee on Friday night.
"When I saw the size of the needle I was about to say, 'No!' " Wright said. "I tried not to look at it but I saw it by accident."
The Trojans are off today, the first day of classes. Practice resumes Tuesday at 4 p.m.