Grothe completed 17-of-30 passes for South Florida (3-0), which will be at home vs. fifth-ranked West Virginia next Friday.
Benjamin Williams had 64 yards rushing on 15 carries with a touchdown, and Amari Jackson caught four balls for 33 yards and a score. Delbert Alvarado booted three field goals and Mike Ford and Jamar Taylor rushed for touchdowns for the Bulls.
T.J. Yates completed only 11-of-27 passes for 85 yards with four interceptions for North Carolina (1-3), which has lost three straight. Yates was sacked four times.
Ryan Houston scored the Tar Heels' only touchdown with a five-yard run.