Smart connected on 6-of-12 shots and distributed three assists for the Cowboys (17-5, 7-3 Big 12), who won for the sixth time in their last seven games.
Markel Brown supplied 17 points and Le'Bryan Nash contributed 14 with nine rebounds for Oklahoma State.
Ioannis Papapetrou finished with 15 points, seven rebounds and four assists, and Demarcus Holland scored 13 for the Longhorns (10-13, 2-8), who have lost eight of their last 10.
Megyn Kelly: Santa Claus and Jesus are both white men
Costly malfunction causes beer flood at Boston-area brewery