Williams also grabbed 11 rebounds and Trevor Mbakwe contributed 12 points for the Golden Gophers (10-1), who nailed down career victory No. 500 for Coach Tubby Smith.
Joe Coleman added 10 points for Minnesota, which led wire-to-wire in picking up its sixth straight win.
Omar Oraby came off the bench to net 15 points and collect four rebounds for the Trojans (3-6).
Byron Wesley added 13 and five for USC.