Allen finished with 145 yards on 21 carries for the Trojans (9-3, 6-2 Pac-12), who overcame frigid conditions in improving to 8-0 all-time against the Buffaloes.
Cody Kessler passed for 184 yards with two touchdowns on 19-of-28 efficiency, but despite the victory, USC lost a shot at the Pac-12 South title when Arizona State downed UCLA earlier Saturday.
Colorado (4-7) was paced by Sefo Liufau, who made good on 17-of-33 passes for 188 yards with two touchdowns and an interception.
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