Isaac Bonton scored 27 points — one off his season high — to lead the Cougars (9-4, 2-4), who dropped their ninth in a row to USC.
Washington State closed to 73-69 with an 11-0 run, highlighted by consecutive 3-pointers from Andrej Jakimovski and Noah Williams, who followed with a three-point play.
Williams again drew the Cougars within four on a 3-pointer, but they could never take the lead.
Eaddy and Evan Mobley scored back-to-back. The Trojans kept a long possession alive with a couple of offensive rebounds before Isaiah White scored under the basket to keep them ahead by 10 points.