Jordan Tolbert provided nine points for the Red Raiders (12-11, 4-6 Big 12), who corralled a second straight victory with the upset.
Robert Turner contributed six points, five steals and three assists.
The Cowboys (16-7, 4-6) struggled again despite 22 points from Marcus Smart, who hurt his team's chances by taking a technical foul with 6.2 seconds remaining.
Smart got into a verbal altercation with a fan sitting in the front row, then lunged at the man and pushed him before being pulled away by players and coaches, ESPN.com reported.
Phil Forte netted 15 points.