Now unranked and without any prospects for a BCS bowl berth, USC finds itself playing the unfamiliar role of spoiler. In No. 1 Notre Dame and USC’s 84th all-time meeting, the Trojans will look to bust the BCS and tarnish what has been a remarkably successful year for the Fighting Irish, considering most pundits predicted 2012 would be a season of transition for the program.

New era · USC coach Lane Kiffin announced Sunday that redshirt freshman quarterback Max Wittek will start against Notre Dame after senior Matt Barkley sprained the AC joint in his right shoulder on a fourth-quarter sack at UCLA. – Carlo Acenas | Daily Trojan

Though losers of three of their last four contests, the downtrodden Trojans can derive solace from the team’s history of ruining opponents’ undefeated seasons. USC has defeated a No. 1-ranked team seven times in its history. Two of those upsets — in 1938 and 1964 — occurred against No. 1 Notre Dame squads at the Coliseum.

USC’s 28-38 loss at UCLA left USC coach Lane Kiffin mostly speechless, as he struggled to explain another substandard outing. The Trojans outgained the Bruins in total yards 513 to 406, took six fewer penalties and sacked budding star quarterback Brett Hundley five times, while only permitting one sack of its own. But USC’s three turnovers — compared to UCLA’s one — proved insurmountable.

“Obviously a very discouraging game,” Kiffin said. “A very tough loss for our fans, for our players and for our staff.”

Adding injury to insult, senior quarterback Matt Barkley — on the one sack USC’s offensive line did relent — suffered a sprain of his right shoulder’s AC joint. Such injuries can require anywhere from two to eight weeks for recovery, so it’s conceivable that the beloved signal caller has seen his career with USC come to a premature end.

“I feel very bad for him and his family,” Kiffin said. “Obviously, this is not the way we pictured the team’s season going.”

Coincidentally, Barkley was also unable to play when Notre Dame last visited the Coliseum after he had suffered a high-ankle sprain. Former quarterback Mitch Mustain filled in for Barkley admirably, passing for 177 yards. Most fans, however, will remember the game as the one in which former wide receiver Ronald Johnson bobbled and dropped a surefire touchdown pass that would have allowed the Trojans to pull out the come-from-behind victory in the waning moments of the game. Instead, USC fell 20-16.

“It’s unfortunate for his career now that two times in a row Notre Dame has come into the Coliseum — and he’s gone to South Bend twice and won — and now he won’t be able to play them at home [ever],” Kiffin said.

Redshirt freshman quarterback Max Wittek will replace Barkley in the starting lineup — a familiar role for Wittek, who succeeded Barkley in high school at Mater Dei.

“We have great confidence in Max,” Kiffin said. “He did well [Saturday] in a very difficult situation. Standing around for 3.5 hours in the rain and to go into that game is not easy to do.”

In limited duty this season against Hawaii, Colorado and UCLA, the 2010 four-star recruit has completed eight of nine passes for a touchdown. Despite Wittek’s lack of experience, Kiffin is confident that he will not have to simplify the game plan too much for the strong-armed gunslinger.

“We would be more apt to do what we normally do with Matt in there,” Kiffin said. “Matt and Max are pretty similar physically, so I think that we will pretty much stick within our system.”

Of course, facing Notre Dame’s stingy defense marks the toughest of first assignments for Wittek. The Fighting Irish rank first in the Football Bowl Subdivision in points allowed per game, surrendering an average of 10.1 per contest. Perhaps most impressively, the Fighting Irish limited Oklahoma, which averages 40.8 points per game, to just 13 points in their Oct. 27 matchup.

Senior linebacker Manti Te’o has deservedly garnered Heisman Trophy buzz, as the bruising defensive captain and former USC fan growing up has snagged six interceptions and racked up 98 tackles this season.

On offense, Notre Dame features dual-threat quarterback Everett Golson, who has completed 59 percent of his passes for 11 touchdowns and five interceptions while adding 258 yards and five touchdowns on the ground. Their two-headed monster of tailbacks Theo Riddick and Cierre Wood have combined for 1,454 yards and tight end Tyler Eifert — a big-time NFL prospect — leads the team in all major receiving categories.

Though the Trojans have faced more well-rounded and potent offenses during the Pac-12 regular season, there’s no question that Notre Dame’s defense will present USC’s offense with its stiffest challenge since the Stanford loss.

Kickoff is scheduled for 5 p.m. Saturday at the Coliseum. The game will be televised nationally on ABC.