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TUCSON, Ariz. -- A momentum-swinging game hanging in the balance, Oregon State coach Mike Riley pulled out a play he had been saving all game.

So what if he would have liked more space to run it. This was the time to do -- and it couldn't have worked out any better.

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• Pac-12 blog

Sean Mannion threw for a career-high 433 yards and hit Connor Hamlett on a 9-yard pass with 1:09 left for his third touchdown, lifting No. 18 Oregon State to wild 38-35 win over Arizona Saturday night.

"I had frankly screwed it up; I was going to call it a little earlier," said Riley, who broke Lon Stiner's school record with his 75th career win at Oregon State. "I was saving that play and wanted it out a little higher, but then we had a good gain. We called it anyway and it came out differently than it ever has, but that's the way we want it right there."

The Beavers sure needed it.

Oregon State (3-0, 1-1 Pac-12) took a 17-0 lead, Arizona charged back and the teams traded scores in the second half of a game filled with big plays and 1,158 yards of combined offense.

Arizona (3-2, 0-1 Pac-12) landed a big blow in the can-you-top this second half, going up 35-31 with 5:34 left when Matt Scott hit Austin Hill on a 7-yard touchdown.

The problem was that it left too much time for Mannion.

Knowing his team had moved the ball all game against the Wildcats, the calm-and-cool sophomore guided the Beavers 75 yards down the field in 10 plays. Facing a third-and-5 with just over a minute left, Mannion called out a play that sent one receiver into the left flat and Hamlett down the sideline. Arizona's defenders followed the receiver in the flat and Mannion whipped a pass to Hamlet, who slipped just inside the pylon for the winning score.

Mannion finished 29 of 45 for the fifth-most passing yards in school history while setting a career high for the second week. He hit Markus Wheaton 10 times for 166 yards and a pair of touchdowns, and Brandin Cooks nine times for 149 yards.

Storm Woods added for 161 yards and a touchdown for the Beavers, off to their first 3-0 start since 2002.

"Arizona's a great team and they came out guns blazing," Beavers cornerback Rashaad Reynolds said. "We had to battle the whole game."

Arizona nearly kept up with them.

Scott fought through a sprained ankle in the second half to throw for a career-high 403 yards and three touchdowns, but had two interceptions, including one near midfield in the final minute. Ka'Deem Carey ran for 115 yards and two touchdowns. Dan Buckner caught six passes for 119 yards and a score.

It wasn't enough for Arizona, which has lost two straight after opening 3-0.

"Losing is losing," Arizona coach Rich Rodriguez said. "The kids are battling and they're going to be all right. Just not right now."

Oregon State had a strange, stop-and-start season before arriving in the desert.

The Beavers had their opener against Nicholls State postponed due to a hurricane, faced a ranked opponent the second week, followed by a bye and another ranked opponent.

They no trouble keeping a rhythm, knocking off No. 13 Wisconsin at home and No. 19 UCLA in the Rose Bowl behind a stingy defense and Mannion's arm.

Oregon State kept the same theme going early against Arizona.

Mannion was sharp early, hitting Cooks on a 57-yard pass in the first quarter to set up a 2-yard touchdown pass to Wheaton in the back of the end zone.

Next series, Mannion hit Wheaton for a 51-yard gain, leading to Trevor Romaine's 30-yard field goal.

Mannion found Kevin Cummings next, on a 38-yard pass to position Tyler Anderson for a 1-yard touchdown dive that put the Beavers up 17-0.

"They had a lot of guys wide open," Rodriguez said. "When we blitzed, we couldn't get to the quarterback and that makes it really tough on our defensive backs."

Arizona's offense tried to answer after sputtering early.

The Beavers bogged Arizona down in the first quarter and held when the Wildcats had their first sustained drive, which ended with John Bonano pushing a 30-yard field goal wide right after Scott was called for intentional grounding.

That wasn't a good sign for the Wildcats, who went 0-for-6 in the red zone in a 49-0 loss to Oregon last week.

Arizona managed to end its red-zone woes late in the second quarter, though, when the officials checked the replay to see if Carey fumbled at the 1-yard line and determined he actually went into the end zone for a score that cut Oregon State's lead to 17-7.

That drive seemed to be the spark the Wildcats needed.

Arizona kept rolling on its opening drive of the second half, quickly marching 91 yards in 10 plays for a 3-yard pass from Scott to Hill.

The Wildcats needed a minute to score again, this one a 24-yard run up the middle by Carey, who carried a couple of Oregon State defenders into the end zone with him to put Arizona up 21-17.

Scott made a mistake on the next drive, when Jordan Poyer missed an interception at midfield, then got it when the ball caromed off Richard Morrison. That set up a 1-yard touchdown run by Woods to give Oregon State the lead back.

Woods followed with a mistake of his own, losing a fumble at Oregon State's 40. Scott then threw to the corner of the end zone to Buckner, who's over-the-shoulder, 16-yard TD catch put the Wildcats up 28-24.

Mannion's turn was next. Using a pump fake, he got the entire right side of Arizona's defense to bite and winged a 20-yard touchdown to Wheaton that put the Beavers back out front.

Scott answered, marching the Wildcats for a 7-yard touchdown pass to Hill, who dived in the final yard to make it 35-31.

He just left too much time for Mannion and the Beavers, who head home to play Washington State next week with plenty of momentum on their side.

"We're definitely enjoying this moment," Woods said. "It took an entire year last years to get where we are today. The sky is the limit for us right now."