Behind forward Derrick Williams’ 22 points and seven rebounds, the Arizona Wildcats overpowered the Oregon State Beavers 78-69 in Staples Center Thursday.

Arizona (26-6) will play the USC Trojans at 7 p.m. tomorrow in the Pacific 10 Conference semi-final round.

Leading 40-37 at halftime, Williams had already scored 16 points, which offset a 19-point first half by Beaver guard Jared Cunningham. The UA defense tightened in the second half, Cunningham scored only four more points, and Arizona forwards Kevin Parrom and Solomon Hill led fast breaks that disallowed the Beaver match-up zone to set up.

Parrom and guard Momo Jones each scored 13 points, and Parrom added four assists in 29 minutes. The sophomore forward started his first game this season in place for guard Kyle Fogg, who came off the bench but was limited by a bruised thigh.

Arizona again shot well from beyond the 3-point arc, going 11-for-21 on the evening.

OSU guard Ahmad Starks picked up the slack for Cunningham in the second half — Cunningham also left for a period with a leg cramp — and scored 17 points for the game.

Mixing up their starting line-up. OSU started 280 pound center Joe Burton against Williams. The Beaver center scored nine points before being thrown out of the game for a flagrant foul on Parrom.