Williams, a senior, had touchdown runs of 26 and 58 yards. His only other 100-yard game came in 2010, when he gained 147 yards on 19 carries against Boise State.
The Aggies (3-1) are off to their best start since winning their first five games in 1978. They've outscored their opponents 51-0 in the first quarter and haven't given up a touchdown in the first half.
They led 17-0 at the break, and it could have been much worse.
After Williams' 26-yard TD run, the Rams (1-3) had a goal-line stand, and Utah State settled for Josh Thompson's 20-yard field goal. The Aggies needed 19 plays to cover 85 yards on their next score, capped by Chuckie Keeton's 1-yard fade pass to Matt Austin on fourth-and-goal from the 1.
Austin fumbled into the end zone in the final minute of the first half, and Colorado State cornerback Shaq Bell scooped it up.
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