Quarterback Sam Darnold threw for five touchdowns - including three to receiver JuJu Smith-Schuster - and USC coasted to a 48-14 victory at Arizona in a Pac-12 game on Saturday.

Darnold threw four scoring passes in the first half, two of which came after Wildcats' turnovers set up the Trojans in the red zone. Smith-Schuster scored with 23 seconds left in the half for a 34-7 lead after he broke five tackles during a 39-yard catch-and-run.

Smith-Schuster also had a 3-yard scoring reception and a 46-yarder on the first possession of the second half. But he headed to the locker room in the second half with an apparent back injury.

USC (4-3, 3-2) won its third consecutive game. Arizona (2-5, 0-4) has lost four consecutive contests for the first time in fifth-year coach Rich Rodriguez's tenure.

With the Wildcats' top two quarterbacks injured, 17-year-old Khalil Tate became the first Arizona true freshman to start at the position since Willie Tuitama in 2005.

Tate had more turnovers (two) than completions (one) in the first half and finished 7 of 18 passing for 58 yards. He also ran 14 times for 72 yards before leaving in the third quarter, replaced by redshirt senior tight end Matt Morin, a former high school quarterback.

Morin completed a 7-yard touchdown pass to receiver Samajie Grant in the fourth quarter.

Darnold, a redshirt freshman making his fourth start, completed 20 of 32 passes for 235 yards and added 54 yards on the ground. Smith-Schuster caught nine passes for 132 yards.

USC starting running back Justin Davis (ankle) did not play, but Aca'Cedric Ware rushed for 103 yards on 12 carries.

About the only thing that went wrong for USC was a botched PAT after its fourth touchdown, with the fumble returned for an apparent two-point play. But the Wildcats committed a personal foul penalty during the return, wiping out the points.

Arizona running back Nick Wilson, limited to eight carries in the past four games because of an ankle injury, managed just six rushes for 47 yards before limping off in the second quarter. He did not play after halftime.

The past nine meetings between the schools had been decided by no more than eight points.

Both teams have byes next weekend.