Nikola Vucevic had 25 points and 12 rebounds, and his teammates came up with two huge blocks in the closing minutes to help Southern California upset No. 10 Arizona 65-57 on Thursday night.
Jio Fontan added 21 points and Alex Stepheson had 12 points and 10 rebounds for the Trojans (16-12, 8-7 Pac-10), who extended their winning streak to a season-best three games.
Jesse Perry scored 12 points and Kevin Parrom added 10 for the Wildcats (23-5, 12-3), whose eight-game winning streak ended on an off-night for offensive star Derrick Williams, who scored a season-low eight points.
The Wildcats head into a showdown at second-place UCLA on Saturday.
Williams' points were well below his average of 19.7, second-best in the league, and it was the first time he was held to single-digits this season. He grabbed 11 rebounds while playing with a wrap protecting his bandaged right pinky finger.
The Wildcats were held below their Pac-10-leading averages in field-goal percentage, 3-point percentage and points scored on the road.
Neither team led by more than four points until the waning minutes. Vucevic hit a pair of free throws to tie it at 56-all with 2:37 remaining.
After Stepheson blocked Lamont Jones on a drive, Stepheson got fouled and made both free throws to put USC ahead 58-56.
Jones got denied again on Arizona's next possession, with Marcus Simmons coming up with a big block. Vucevic was fouled again and made both, extended USC's lead to 60-56 as the crowd chanted, "Go SC!" with 58 seconds left.
Fouled by Simmons, Kyle Fogg made the second of two free throws to leave Arizona trailing by three with 40 seconds left. Parrom and Williams missed on the same possession, forcing the Wildcats to foul the rest of the way.
The Wildcats fell to 1-4 at Galen Center. The Trojans, whose field-goal percentage defense of .411 is second-best in the league, held Arizona to 36 percent.
Williams didn't score his first basket until there was 5:15 left in the half, giving the Wildcats their largest lead of eight points.