TCU (32-14) jumped on Propst early as the Horned Frogs opened the game with four-straight hits. After back-to-back singles, Taylor Featherston put the visitors on the scoreboard with a two-RBI triple, and Jason Coats followed that with a single to make the score 3-0.
Propst escaped the first without any further damage, and the Cowboys tallied a run in the bottom of the inning off TCU starter Erik Miller on an RBI groundout by Zach Johnson.
But the Horned Frogs added to their lead in the fourth. Josh Elander led off the frame with a double, and two batters later, Joe Weik delivered the first of his two home runs in the game, a blast that gave TCU a 5-1 lead.
That advantage reached 6-1 when Weik led off the seventh with another round tripper before OSU used a home run of its own in the bottom of the inning, a solo shot by Mark Ginther, to cut its deficit to 6-2.
OSU threatened a rally in the eighth. Singles by Zach Johnson and Davis Duren put Cowboys on first and third with one out, but Duren was picked off first and Ginther grounded out to end the threat.
The Horned Frogs put the game away in the ninth inning as they tagged OSU reliever Ian McCarthy for four runs on four hits.
Miller picked up the win for TCU to improve to 5-6 as he worked 7.1 innings and allowed two runs on nine hits.
The two teams will battle in the rubber match of the series Sunday at 1:06 p.m. in a game that will be nationally televised by Fox College Sports.