Wallace completed 17-of-25 passes for 177 yards and gained 57 yards on 12 carries for Ole Miss (3-0).
Scott scored a touchdown while carrying the ball 19 times.
Case McCoy was held to 196 yards and a TD on 24-for-36 passing for the Longhorns (1-2), who have lost two straight.
Jonathan Gray paced Texas' rushing attack with a 91 yards and a score on 19 carries.
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