Justin Campbell pitched six innings, gave up three hits and struck out seven batters and No. 4-seed Oklahoma State beat fifth-seeded Oklahoma 9-5 on Wednesday night.
The Cowboys (33-16-1) advance to play No. 8-seed West Virginia in a second-round game of the Big 12 Tournament on Thursday.
Oklahoma takes on top-seeded Texas on Thursday in an elimination game. The Mountaineers beat the Longhorns 5-1 5-1 earlier Wednesday.
Lead-off batter Caeden Trenkle got Oklahoma State started hitting a 1-0 pitch to center field in the bottom of the first. Three innings later, Matt Golda hit a solo homer for a 2-0 lead. The Cowboys put four on the board in the fifth and three in seventh to just miss ending it on the 10-run rule.
Oklahoma scored all its runs in the ninth with just one hit. Peyton Graham went 3-for-5 for the Sooners (27-27) and drove in a pair of runs.