LOS ANGELES — Freshman O.J. Mayo scored 23 points, and Southern California turned up its defense down the stretch today to beat Arizona State 59-55 in the quarterfinals of the Pac-10 tournament.

Freshman Davon Jefferson and Taj Gibson each had 11 points and nine rebounds for the Trojans, who held the Sun Devils without a field goal after Derek Glasser made his only basket of the game with 9:35 remaining.

The win was the sixth in seven games for the fourth-seeded Trojans (21-10), who had already assured themselves of an NCAA tournament berth.

It appeared that fifth-seeded ASU (19-12) needed at least one victory in the Pac-10 tournament to earn its first NCAA tournament berth in five years. The Sun Devils lost 10 of their last 15 regular-season games.

Freshman James Harden led the Sun Devils with 16 points. Jeff Pendergraph added 13 points and six rebounds and freshman Rihards Kuksiks scored 12 for ASU, which shot 28.6 percent in the second half and 35.3 percent overall.

USC shot 42.9 percent and outrebounded ASU 36-26. The Trojans won despite committing 19 turnovers to 12 for ASU.

A three-point play by Jefferson with 5:11 remaining snapped a 53-all tie and put USC ahead for good. The Trojans wouldn't make another field goal, but they still managed to win.

A foul shot by Gibson with 4:32 left gave USC a four-point lead, and neither team scored after that until Pendergraph made a foul shot with 2:10 to play.

Ty Abbott added another free throw with 1:38 left to make it 57-55, and after a miss by Mayo and a failed follow shot by Gibson, Glasser's pass went out of bounds, prompting USC's Daniel Hackett to high-five a fan in the front row.

After another USC turnover, the Sun Devils raced downcourt and Harden missed from close range. Pendergraph slammed the ball into the basket to apparently tie the game with 16.9 seconds to go, but was called for his fifth foul going over the back of Jefferson, nulllifying the basekt.

Jefferson made two free throws to complete the scoring.

The Sun Devils outscored the Trojans 11-4 to start the second half for a 43-38 lead, and extended their advantage to seven before a basket by Gibson and five straight points by Mayo tied it at 49 with 7:53 to play.

Neither team led by more than four points after that.

Harden scored eight points during an 11-2 run that put the Sun Devils ahead 17-9. The Trojans scored the next 10 points for a two-point lead. Neither team led by more than four points during the remainder of the first half, which ended with USC on top 34-32.

The Trojans shot 54.5 percent to Arizona State's 40 percent and outrebounded the Sun Devils 20-10 in the half, but committed 12 turnovers to ASU's four. Mayo had 14 points, five assists and four turnovers at halftime.

The teams split their two regular-season games, with each winning by 14 points at home.