EUGENE (AP) - The Oregon Ducks got more than a needed win over Portland State, they got a glimpse into the future.

When the 55-12 victory over the Division I-AA Vikings was well in hand, the Ducks gave true freshman Nathan Costa a chance to play.

Costa came into the game when Oregon was ahead, 48-12, and went 3-for-3 for 51 yards. He led the Ducks on a drive that ended with Andiel Brown's 7-yard scoring run and the final margin.

"He is a very efficient quarterback,'' coach Mike Bellotti said. "He fits this system very well.''

Costa also played in a spread-option offense at Hilmar High School in California.

"It all seemed like I was playing again in high school,'' he said. "It didn't seem a lot faster, it didn't seem any different.''

Costa is one of three freshman quarterbacks for the Ducks, joining John Roper and Cody Kempt. With Dennis Dixon a junior, the three for now are battling for the starter's job in 2008.

While the Ducks got to see Costa, the win was also important because it made Oregon (5-2, 3-2 Pac-10) bowl eligible. The Ducks, coming off a loss at Washington State, rose from No. 25 to No. 24 in rankings.

But it was at a cost: star running back Jonathan Stewart, already battling sore ankles, went out of the game with an abdominal strain and sore ribs.

Stewart was injured on his first carry when he was dragged well out of bounds by Portland State safety Charles Manigo. No flag was thrown.

"It fired me up because it was unnecessary,'' teammate Jeremiah Johnson said. "That's like a brother to me. It came to be a little personal, instead of just going out there and playing a ballgame. (Stewart) just told me to go out there and go get 'em.''

Johnson did, scoring on runs of 1, 6 and 1 yards in the first half.

Portland State's Mu'Ammar Ali kept it close, rushing for 127 yards in the first half, including a 57-yard TD run to bring the Vikings within 21-12 early in the second quarter.

Johnson quickly answered with two touchdowns in the final 4:15 of the first half for a 35-12 lead.

Dennis Dixon completed 13 of 23 passes for 150 yards and one TD. He also rushed for 42 yards on six carries.

Jaison Williams had eight catches for 112 yards and a touchdown.

Next for the Ducks is Washington (4-5, 2-4) on Saturday at Autzen Stadium.