Dixon, Oregon's gifted starting quarterback, hurt his left knee in the first quarter, about 7 minutes after he ran 39 yards for a touchdown. Dixon crumpled to the turf without being touched.
"My foot got planted in the ground, and my knee went the other way," Dixon told ESPN toward the end of the game.
Antoine Cason returned a punt 56 yards for a touchdown and an interception 42 yards for another score as the Wildcats (5-6, 4-4) shook up the national title race.
Brady Leaf, who replaced Dixon, completed 22 of 46 passes for 163 yards and threw two interceptions.
Arizona quarterback Willie Tuitama completed 21 of 39 passes for 266 yards and two touchdowns.
* Despite speculation to the contrary, Nebraska interim athletic director Tom Osborne said he has not made a final decision on coach Bill Callahan.
Osborne said he plans to meet with Callahan on Nov. 24, the day after Nebraska (5-6) plays at Colorado.
* Louisville defensive end Deantwan "Peanut" Whitehead's football career has ended due to a spinal condition that showed up after an injury in last week's loss to West Virginia. *