SMU (7-5) had matched its biggest lead of the game when Robert Nyakundi made three free throws for a 58-52 advantage with 1:17 left in the first overtime. Keiton Page then made two 3-pointers in a span of 33 seconds, with a miss by Nyakundi between those shots.
Guerrero opened the second overtime with a 16-foot jumper, then made a 3-pointer and had a driving layup to stretch the lead to 65-58.
Page led Oklahoma State with 27 points.
Nyakundi had 20 points and 11 rebounds for SMU, which has lost 10 in a row against the Cowboys.