USC thought its running game was out of the woods after LaVale Woods' 129-yard performance against California.
But Woods sprained his left ankle on the second possession of USC's game against UNLV Saturday, and he came out for the second half in street clothes, even though X-rays were negative.
That left USC's running attack to freshman Malaefou MacKenzie and senior Delon Washington, who had been dumped for Woods a week earlier.
MacKenzie, from Capistrano Valley High, carried the load, running for 104 yards in 19 carries and two touchdowns.
Adam Abrams held onto USC's kicking job after Coach John Robinson staged a competition this week between Abrams and backup Adam Rendon.
Abrams came through with USC's first field goals of the season against UNLV, making two in the final three minutes of the first half, one from 27 yards and the other from 37.
Abrams, a three-year starter, was inconsistent last season and missed a 34-yarder and an extra point against California, prompting the competition.
USC cornerback Daylon McCutcheon's first big offensive play of the season came late in the first quarter when he picked up nine yards on a reverse, showing why USC wants to get the ball in his hands.
R. Jay Soward handed off to McCutcheon, who twice eluded UNLV defensive back Randy Black before running out of room on the sideline.
With the offense struggling, the Trojans plan to utilize McCutcheon more and more on offense as a receiver or slot back.
He rushed for 2,456 yards as a senior at La Puente Bishop Amat High in 1994 but chose to play cornerback in college because his pro prospects are better at that position.
Ted Iacenda, a redshirt freshman, started a second consecutive game at fullback for USC over senior Rodney Sermons.