Notre Dame enters the final quarter trailing USC 24-10.
Notre Dame was ready to tie the game with USC, but the Irish were bit by the turnover bug again at the worst time.
Dayne Crist, who stepped in for Tommy Rees when the starting quarterback hurt his knee on the drive, fumbled the snap from the Trojans' 1-yard line.
The ball squirted back to the 20 where Jawanza Starling picked it up and ran 80 yards for a touchdown and a 24-10 lead.
Crist briefly took over for Rees after the sophomore moved the Irish to the Trojans' 39 where he injured his right knee when USC's Devon Kennard fell on him.
Crist, who opened the season as the starting quarterback, moved the Irish to the 3-yard line by throwing for 36 yards. After change-of-pace quarterback Andrew Hendrix ran for 2 yards, Crist went back in and the snap got away from him.
Rees came back in for the final series of the third quarter, completing two passes for 22 yards to put the Irish at the Trojans' 42 to start the final quarter.