Kansas State left fielder Jon Davis tripled and scored the tying run in the bottom of the eighth on a squeeze play, and right fielder Tanner Witt plated the go-ahead run, second baseman Ross Kivett, moments later on his RBI single to right.
And with that, OU's four-game winning streak is over, and they'll have to rebound if they hope to win the rubber match of the series at 1 p.m. Sunday.
"This is a tough game to lose," said OU first baseman Hunter Lockwood, who paced the Sooner offense with five RBIs on a 2-for-5 performance at the plate. "You know, we go up finally. Go down in the beginning, come up late and then lose it a little bit later in the game, but you know, I think it will just give us the motivation to come out and play really well tomorrow."
Kansas State seized a 4-0 lead after just the third inning in this one.
An RBI single each from catcher Dan Klein and shortstop Jake Brown made it 2-0 in the second.
Wildcat third baseman Matt Giller's sacrifice fly, followed up with an RBI double by designated hitter Blair DeBord, upped it to the early four-run lead.
The Sooners, beneficiaries on an errant throw by the Kansas State first baseman, quickly cut into it in the bottom of the fourth.
Moments after that error, Lockwood hammered a double to the 411 sign in right center, scoring two.
He scored and made it a 4-3 game on shortstop Caleb Bushyhead's RBI single a batter later.
The Wildcats extended it back out to a three-run advantage in the following half inning when DeBord recorded his second and third RBIs of the day on a two-run blast to left.
But OU came back in the bottom half and took its first lead of the day, thanks to a home run of its own.
After third baseman Garrett Carey doubled to lead off the inning and was plated on second baseman Jack Mayfield's RBI single, Lockwood sliced a three-run bomb inside the right field foul pole to put the Sooners up 7-6.
"Just trying to put good swings on it and hit it the other way," Lockwood said. "Try to just do that to the best of my ability up until the last at bat I just kinda fell away from my approach a little bit."
Lockwood struck out to end the game, but at the time of his homer, it didn't seem like that would be the case.
However, the Sooner bullpen couldn't close it out, as reliever Steven Okert gave up the lead in that eighth and took the loss, despite striking out four in his 2 1/3 innings of work.
Kansas State pitcher Gerardo Esquivel recorded the win after coming in for four innings of relief work and surrendering two earned runs, while striking out two.
Wildcat closer Nate Williams worked a scoreless ninth and picked up the save.