Updated

A week after Oregon State relied on its offense for a victory over Arizona, the defense helped secure the win against Washington State.

The Beavers improved their record to 4-0 (3-0 in the Pac-12) and jumped four spots in The Associated Press rankings to No. 10 after a 19-6 win at home over the Cougars on Saturday.

"Our record says we are perfect right now, and I can't argue with that," said Oregon State receiver Markus Wheaton. "But we have a lot to work on. As you can see there are a lot of penalties and missed assignments."

There were also turnovers. Sophomore Sean Mannion was 25 of 42 for 270 yards, but he threw three interceptions to kill promising drives. Add that to 11 penalties for 110 yards, and the Beavers were their own worst enemies at times.

The first half was particularly trying, with Mannion throwing two of his INTs and another drive stalling at the Cougars 24 when the Beavers failed to convert on fourth-and-2. They took a tenuous 6-3 lead into halftime.

"I'm really proud of the way our team came out in the second half," Mannion said. "I think that says a lot about us."

Led by cornerback Jordan Poyer and his three interceptions, the defense was sensational, driving Cougars quarterback Connor Halliday from the game after the second drive of the third quarter. Beavers defensive end Scott Crichton sacked Halliday's replacement, Jeff Tuel, three times.

The Cougars' "Air Raid" offense under coach Mike Leach was held to 207 yards passing and just 20 yards on the ground. Washington State (2-4, 0-3) had five turnovers — four interceptions and a fumble.

After wins over Wisconsin, UCLA, Arizona and the Cougars, the Beavers haven't had both the defense and offense clicking at the same time.

"We have so much potential to win every game on our schedule," Crichton said. "We haven't played as a whole team yet because either the offense or defense carries us in each game. Once we finally play as a team, you guys are in for something great."

The Beavers are 4-0 for the first time since 2002. They haven't started a season 5-0 since 1939. Even the Fiesta Bowl champions of 2000, who finished 11-1, lost their fifth game.

Oregon State travels to BYU on Saturday. These Cougars (4-2), survived a scare Friday night against Utah State, narrowly winning the battle for the Old Wagon Wheel 6-3. BYU features a stingy defense that has held opponents to under 300 yards of total offense in 12 straight games.

To play a truly complete game, the Beavers will have to end that streak. And while OSU is 2-0 on the road this season, having beaten UCLA at the Rose Bowl and Arizona in Tucson, LaVell Edwards Stadium — with an elevation of 4,600 feet and a rabid crowd — will likely be the most inhospitable venue the Beavers have seen this year.

"Man, I can't wait to put together a full game," running back Storm Woods said, "and see how good we are."