TUCSON, Ariz. -- Sam Darnold threw for five touchdowns -- three to Julu Smith-Schuster -- to lead USC to a 48-14 rout of Arizona on Saturday, the Trojans' third straight Pac-12 victory.

Darnold, a redshirt freshman who didn't start until the fourth game of the season, completed 20 of 32 attempts for 235 yards and ran for 54 yards in six carries before sitting out the fourth quarter. He threw for 186 yards and four scores as USC built a 34-7 halftime lead.

Smith-Schuster finished with nine catches for 132 yards.

The Trojans (4-3, 3-2 Pac-12) rolled for 575 yards and remained a half-game out of first place in the Pac-12 South. Arizona (2-5, 0-4) lost its fourth in a row.

Wildcats true freshman Khalil Tate completed 7 of 18 passes for 58 yards in his first collegiate start. Playing in place of injured Brandon Dawkins, Tate threw an interception and fumbled the ball away, leading to two USC touchdowns. He ran for 72 yards and a touchdown on 14 carries.