updated 10:08 p.m. ET Nov. 15, 2007

TUCSON, Ariz. - Oregon’s national title dream has ended.

Quarterback Dennis Dixon’s Heisman Trophy campaign also took a heavy blow.

The curse of No. 2 claimed another victim when the second-ranked Ducks lost Dixon to a knee injury and never recovered in a 34-24 upset by Arizona on Thursday night.

“The national championship thing was fine while it lasted,” Oregon coach Mike Bellotti said. “The reality is we’re still always trying to get the conference championship and the very best bowl game (the Rose Bowl).”

Oregon (8-2, 5-2 Pac-10) became the fifth No. 2 team to lose since Oct. 6, following USC, California, South Florida and Boston College. The Ducks’ defeat could open the door for third-ranked Oklahoma in The Associated Press Top 25 poll, and for No. 3 Kansas in the Bowl Championship Series standings.

Dixon, Oregon’s gifted starting quarterback, hurt his left knee on an option play in the first quarter. Dixon crumpled to the turf without being touched and took Oregon’s national championship hopes with him.

Dixon sprained the same knee on Nov. 3 against Arizona State. Dixon wore a brace but said he felt good in warm-ups, and he flashed his usual explosiveness in a 39-yard touchdown run on the game’s opening series.

“Coming into this game, I felt totally confident,” he said. “My foot got caught in the ground. That’s just the way football is.”

Bellotti said he didn’t know if Dixon, a senior, might be lost for the season. He didn’t seem confident Dixon would return for Oregon’s next game at UCLA on Nov. 24.

“It’s obviously not a happy deal,” Bellotti said.

Dixon said he would undergo tests on Friday, and he hadn’t considered that his college career might be over.

“If that’s the case, it’s going to be hard to swallow that,” said Dixon, who was consoled on the bench by his father, Dennis Dixon Sr. “You’ve got to play your heart out, because you never know when you’re going to get that last play.”

Antoine Cason returned a punt 56 yards for a touchdown and an interception 42 yards for another score as the Wildcats shook up the national title race on a cool night in the desert. Red-clad students poured out of the grandstand as the Wildcats (5-6, 4-4) ambushed a ranked team in Arizona Stadium for the fourth straight season under coach Mike Stoops — all in November.

“November has been good to us,” Stoops said. “It is nice to show what kind of team we have at Arizona.”

Stoops’ future appeared to be in jeopardy only a month go. It isn’t now.

“I am so proud of all of the coaches and players,” he said. “Everyone played great tonight, but we definitely had to earn it.”

Brady Leaf, who replaced Dixon, completed 22 of 46 passes for 163 yards and threw two interceptions.

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“I’m a little disappointed in the way I played,” said Leaf, who stayed in the game despite spraining his ankle early in the second half.

Dixon finished 5-for-8 for 62 yards, and threw an interception. He carried twice for 34 yards.

Arizona quarterback Willie Tuitama completed 21 of 39 passes for 266 yards and two touchdowns, and was intercepted once. Mike Thomas caught two touchdown passes for the Wildcats.

Oregon’s Jonathan Stewart carried 28 times for 131 yards.

Early on, Oregon appeared to be on cruise control with Dixon running its potent offense, which came in averaging 42.8 points, fifth in the nation.

On fourth-and-3 at the Arizona 39, Dixon froze the defense with a fake to Stewart, burst through a hole in the right side and ran untouched to the end zone. Ed Dickson ran for the 2-point conversion to put the Ducks ahead 8-0.

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