Crabbe scored 19 points in the second half, including seven straight, for the Bears (9-5, 1-1 Pac-12). He went 9 for 12 from the field and made all eight free-throw attempts.
Wallace made two 3-pointers during a surge that gave Cal a 66-58 lead. The Bears, who went 0 for 19 from 3-point range in their previous two games, made 5 of 9 from beyond the arc.
USC was denied its first three-game winning streak since February 2011.
Crabbe singlehandedly sent Cal on a 7-2 run halfway through the second half when he made four free throws and a 3-pointer for a 53-47 lead.