Oregon State played up the underdog role all season and is now the latest No. 12 seed to win an opening-round NCAA Tournament game.
Roman Silva scored 16 points and the Beavers took advantage of Tennessee's icy perimeter shooting to beat the fifth-seeded Vols 70-56 in the Midwest Region.
Oregon State became the first Pac-10/12 school to win the conference tournament after being picked to finish last and is now the 51st 12-seed to take down a five-seed since the NCAA Tournament bracket expanded in 1985.
The Vols shot 5 for 26 from the arc while shooting 33% overall.
The Beavers will face the winner of the Oklahoma State/Liberty game.