First, quarterback Mark Sanchez left after his junior season for the NFL, creating a chance for the early high school graduate to immediately compete for the starting job.
Barkley narrowly lost out to sophomore Aaron Corp in the spring, but the precocious 18-year-old leaped into the front-runner position on Wednesday when the Trojans learned that Corp could be sidelined for up to three weeks because of a leg injury.
USC opens its season Sept. 5 against San Jose State at the Coliseum. If Barkley takes command of the position, he could become the first true freshman quarterback in USC history to start an opener.
"I don't think there's pressure on me at all, at least I don't feel any," Barkley said after practice. "It's just exciting. I love football and this is a chance, an opportunity that's been placed in front of me and I've just got to grab hold of it."
Coach Pete Carroll said the Trojans, ranked fourth in the USA Today/ESPN preseason coaches' poll, were not "rocked" by Corp's injury or the situation.
"As always, it creates a great opportunity for Matt to feel like he's the guy and feel like he's in charge for whatever the length of time is here," Carroll said. "And it's important for him to do that to show us, to feel it, and to show his teammates too."
Barkley and junior Mitch Mustain took the first-team snaps on Wednesday.
Corp underwent an MRI exam earlier in the day to gauge the damage incurred Monday when a defensive lineman rolled into his left leg. Tests showed no ligament damage but revealed a cracked fibula.
Corp said he could be sidelined from one to three weeks.
"It's kind of a best-case scenario, it seems like, with the type of injury I had," he said. "I'm excited that it's not anything season-ending or even months [sitting out] or anything like that. I'll just rehab and get back out there as soon as I can."
Corp said his injury wouldn't prevent him from throwing, so he was confident he would be able to keep his arm in shape.
"I'm going to be wearing a [knee] brace so that might affect my mobility a little," he said. "But . . . I'm going to come back when I'm ready and I can do everything in the offense."
Last season, USC went through a similar scenario when Sanchez dislocated a kneecap on the third day of camp. The injury created a competition between Corp and Mustain to possibly start the opener at Virginia, but Sanchez returned to practice about a week before the game and did not relinquish the position.
Carroll acknowledged that Sanchez, who started three games in 2007, was "clearly the No. 1 guy," when injured, a status Corp does not similarly enjoy over Barkley, a four-year starter at Santa Ana Mater Dei High.
"I think this competition is obvious," Carroll said. "We see it every day and Aaron knows that and Matt knows that, so I think it's a little bit different."
Saying that it was important for Corp to "keep his mind right," Carroll added, "He can't drift off and lose what he has gained in terms of installation and understanding and verbiage and communication. He needs to stay really fresh because that's what his job is as we keep moving."
Offensive lineman Jeff Byers spun the injury into a win-win situation for both of USC's top quarterbacks.
"It gives Matt Barkley a great chance to come out and compete and take a job," Byers said. "It should be motivation for Corp to understand the complete offense and really hone down the mental part of the game.
"I don't think it's a big deal. . . . People get hurt every day. That's why we're SC. We recruit the best players around the country and when a guy goes down we've got another All-American to step up in his place."
Mustain, who was 8-0 as a freshman starter at Arkansas in 2006, also plans to make a run at the starting job.
"I don't know what anybody else's attitude is," he said. "But I'm going to go at it like I've got an opportunity to pick something up and run with it and leave the truth of that to the guys who are in charge."