Nash was the only player in double figures for the Cowboys, but they shot 55 percent from the floor and limited TCU to 16 field goals for the entire game.
Oklahoma State led by just three with 5 minutes to go in the first half, then finished the opening period on a 12-1 run to take control.
The Cowboys (21-6, 11-4 Big 12 Conference) are one game behind co-leaders Kansas and Kansas State in the league race.
Kyan Anderson scored 15 points to lead the Horned Frogs (10-17, 1-14), whose only conference win came against Kansas.
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