Le'Bryan Nash netted 24 points and Marcus Smart added 21, as 13th ranked Oklahoma State beat No. 9 Kansas State, 76-70.
Markel Brown finished with 16 points for Oklahoma State (23-7, 13-5 Big 12), which bounced back from Wednesday's loss at Iowa State to clinch the third seed in next week's conference tournament.
Coming into Saturday, only Kansas' .940 winning percentage at home was better than the Cowboys' .864 mark since the Big 12 was formed in 1996-97.
Despite the loss, Kansas State (25-6, 14-4) claimed a split of the Big 12 regular-season crown later Saturday when Kansas lost at Baylor. The Wildcats hadn't won a conference title since 1976-77, when the Big 12 was known as the Big 8.
Rodney McGruder led K-State with 22 points, while Thomas Gipson chipped in 15.
McGruder's 3-point play with 4:45 to go gave the Wildcats a 61-57 lead, but the Cowboys countered with a 14-1 run to put the game away.
"There were a couple bad plays that we could have stopped. That's on us," McGruder said.
Smart hit a jumper and two free throws on back-to-back possessions to tie it before Nash's layup staked the hosts to a 63-61 advantage with 2:48 remaining.
Four Brown foul shots, sandwiched around McGruder splitting a pair from the stripe, upped the margin to 67-62 with 1:03 remaining, and Oklahoma State sunk nine of their final 10 shots from the foul line to seal the victory.
The Cowboys netted the final four points of the first half to head into the break with a 36-30 cushion.
However, Angel Rodriguez had six points during a 14-1 Wildcats' second-half run that gave them a 50-41 spread with 13:14 to go.
"We knew we had to get our way back into the game. We took it one possession at a time," Brown said. "We got stops on the defensive end and converted them into offense. We just went out and got the momentum back."
McGruder tallied 26 of his season-high 28 points in the second half of a 73-67 Wildcats' win over the Cowboys on Jan. 5 ... Oklahoma State shot 56.8 percent (25-of-44) from the floor.