Parker Scott earned the win for third-seeded Oklahoma State (33-17). He gave up one run and four hits in six innings.
All-Big 12 pitcher Nick Lodolo took the loss for sixth-seeded TCU (29-25). The left-hander pitched seven innings and gave up five runs on five hits.
Simpson homered in the bottom of the second inning to put Oklahoma State up 1-0. Hunter Wolfe answered for TCU in the third with a solo shot to tie the score.
Oklahoma State broke the game open with four runs in the sixth, highlighted by Trevor Boone's two-run homer. TCU tried to rally but scored just one run in the ninth.
In Thursday's action, Oklahoma State will play Baylor while TCU will face Oklahoma in an elimination game.
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