Mathews opened the OT period with a 3-pointer, his first make on seven attempts from beyond the arc. But two layups and three free throws from Josh Adams gave Wyoming a 69-67 lead with 2:44 left, its first lead since 3:32 in the first half.
A jumper from Mathews evened it at 69-all, and he made 3 of 4 free throws in the final six seconds to clinch the win for Cal (6-2).
Adams finished with 32 points on 10-of-21 shooting for the Cowboys (5-3).
The Golden Bears made just 9 of 24 second-half shots, including an 0-for-7 stretch in the final 5:25 in which they were outscored 13-3. Wallace had a chance put the Bears ahead with five seconds left, but his potential game-winning jumper fell short.