After Kathleen Nash's fourth 3 pointer of the game gave Texas (21-12) a 72-71 lead, Riley drove coast to coast to put Oklahoma State on top. After neither team could score, Carla Cortijo had a chance to win it for the Longhorns when she drove the lane with 10 seconds left but was whistled for an offensive foul.
Shaunte' Smith, who took the charge, hit two free throws to put the Cowgirls up by three, and Cortijo then missed a tying 3-pointer at the buzzer. Smith finished with 12 points and 16 rebounds for Oklahoma State, which was the 13th ranked opponent that Texas faced this season.
The Longhorns, who trailed by 16 points at halftime on Wednesday night before rallying to stun No. 8 Baylor in the biggest halftime comeback in the history of the tournament, trailed 46-34 at the break before once again turning it around in the second half.
A day after opening up the final 20 minutes with a 19-3 run to tie the game against the Bears, Texas strung a 16-6 run together to start the second half to pull to 52-50 on a 3-pointer from Cortijo.
Texas took its first lead since the score was 4-2 when a 3 by Nash gave the Longhorns a 55-54 lead with 13 minutes left in the game.
After the teams traded baskets, Green hit two straight jumpers and made a pass from the seat of her pants to Riley, who knocked down a 3 from the corner to give Oklahoma State the lead again at 69-67 with 3:50 left.
Nash and Cortijo led Texas with 14 points each and Earnesia Williams added 12 points and seven boards for the Longhorns, who will await word on their NCAA tournament seed on Monday.
The Cowgirls led by one point, 11-10, before Texas missed 12 of 14 shots to fall behind 28-14. The 17-4 run by Oklahoma State was fueled by eight points from Riley, including a jumper with 9:04 left in the half that capped the run and forced a timeout from Texas coach Gail Goestenkors.