Chynna Brown led Texas Tech with 15 points and hit the game-winning three.
Kelsi Baker had 14 points and six rebounds as the Lady Raiders (11-2) stopped Oklahoma State's winning streak at 17 games. The streak, which extended to last season's Cowgirls WNIT title, had been the longest in the nation.
Monique Smalls scored 12 points. Smalls and Casey Morris made two free throws apiece down the stretch for Texas Tech, which has won four of the last five in the series against OSU.
Tiffany Bias led the Cowgirls (11-1) with 27 points and Toni Young had 12 points and 12 rebounds before fouling out. The Cowgirls led 18-3 just 8 minutes into the game, but Texas Tech came back to lead 32-27 at halftime following a 29-9 run.