Williams carried the ball 18 times and tallied all three of his scores during a big fourth quarter for the Aggies (11-2), who wrapped up the most successful season in the program's history.
Chuckie Keeton went 21-of-31 for 227 passing yards and added 92 yards rushing with a score in the victory.
Matt Austin led the Utah State receiving corps with six grabs for 76 yards.
Austin Dantin managed to complete 13-of-22 passes for 133 yards with two pickoffs for the Rockets (9-4).
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