Shaina Pellington and Jade Loville each had 17 points for the Wildcats (18-5, 8-4 Pac-12 Conference), who picked up a critical sweep in Los Angeles after beating No. 14 UCLA 71-66 in overtime Friday.
Helena Pueyo had her only two points from the foul line with 15 seconds to go for a 77-73 Arizona lead, the first time it became a two-possession game in the second overtime.
The Wildcats had a four-point lead midway through the first overtime but the Trojans scored six straight before Maya Nnaji tied it at 68 with 5.2 seconds left.
Arizona had a five-point lead in regulation with just over two minutes to go but Rokia Doumbia hit a three-pointer and a layup to tie it and Destiny Littleton made a pair of free throws after an offensive rebound to put USC up 58-56 with 43 seconds to go.
Loville quickly answered. The Trojans missed a shot with six seconds to go but Arizona couldn’t get off a final shot.
Littleton had 21 points for the Trojans (17-6, 7-5), playing all 50 minutes, as did Kadi Sissoko, who scored 15 points. Rayah Marshall had 17 points, 20 rebounds and six blocks in 48 minutes. Doumbia, a senior transfer from Purdue, had a career-high 17 in 28 minutes off the bench before fouling out in the first overtime.
USC went four of 13 from the field and nine of 10 from the foul line in the two overtimes. Arizona was seven of 15 with three threes and made six of eight free throws.
Reese, who had only eight points at halftime, and Pellington, who had four, played 49 minutes.
Arizona is home Friday against No. 2 Stanford, which will drop after losing 72-67 at Washington Sunday when USC goes to Oregon.