Published: Oct 21, 2012 1:56 AM EDT
Updated: Oct 21, 2012 6:32 AM EDT

CORVALLIS, Ore. (AP) - Oregon State's defense helped out when quarterback Cody Vaz struggled in the rain, and the No. 8 Beavers remained undefeated with a 21-7 victory over Utah on Saturday night that gave them their best start in more than a century.

Vaz made his debut last weekend as Oregon State's starter and threw for three touchdowns against BYU to earn Pac-12 player of the week honors. This time, he passed for 174 yards against the Utes. But the Beavers' defense had an interception and a fumble recovery that led to two first-half touchdown runs by Storm Woods.

Woods had 17 carries for 46 yards and all three touchdowns for Oregon State (6-0, 4-0 Pac-12), which hadn't opened a season 6-0 since 1907, when the school was the Oregon Agricultural College. The victory also meant bowl eligibility for the Beavers, who went 3-9 last season and were picked to finish last in the Pac-12 North this year.

Freshman Travis Wilson threw for 172 yards and a touchdown for Utah (2-5, 0-4), which opened conference play with four consecutive losses for the second straight season.

Vaz started a second consecutive game in place of Sean Mannion, who had surgery to repair meniscus in his left knee a little more than a week ago. Mannion was already back at practice and was Vaz's backup against the Utes.

Vaz made his first start since high school last weekend and threw for 332 yards in Oregon State's 42-24 victory over the Cougars. Against the Utes he completed 16 of 26 passes but looked shaky at times in the periodic rain.

Oregon State also struggled with its ground game, rushing for just 52 yards. So instead, the Beavers relied on their defense.

Oregon State capitalized on Michael Doctor's interception of Wilson with a 1-yard scoring run from Woods, putting the Beavers ahead 7-0 late in the first quarter. Rudolf Fifita then sacked Wilson and forced a fumble that was recovered by Dylan Wynn, leading to Woods' 2-yard touchdown dash.

Wilson found Jake Murphy with an 18-yard scoring pass midway through the second quarter for the Utes' lone touchdown. Coleman Petersen missed a 43-yard field goal on Utah's first possession.

Utah threatened in the third quarter and got as close as the Oregon State 3, but DeVonte Christopher's fumble was recovered by Scott Crichton to end it.

With Mannion standing on the sidelines with his helmet on, Vaz got rolling with an efficient fourth-quarter drive that ended with Woods' 3-yard touchdown dive. Wilson answered with a drive of his own that stalled when he was sacked for a loss on fourth-and-9 on the Oregon State 18.

Sean Martin intercepted Wilson on Utah's final drive of the game.

Wilson passed for 220 yards in his first career start last week, a 21-14 loss to UCLA. Coach Kyle Wittingham decided to stick with him this week over senior Jon Hays, who started three games this season after Jordan Wynn went down with a career-ending shoulder injury. Hays threw for two touchdowns against the Beavers last season, the Utes' first in the expanded Pac-12 Conference.

Last season the Utes ended their four-game skid to open conference play with a 27-8 victory over Oregon State that touched off a four-game winning streak.

Utah had won four of its last five games against the Beavers.