KANSAS CITY, Mo. — Keiton Page scored 19 of his 24 points in a dominating first half, and Oklahoma State withstood a brief rally in the season's third Bedlam game to beat Oklahoma 81-67 on Wednesday night in the opening round of the Big 12 Tournament.Oklahoma State (22-9) raced to an 18-point lead in the first six minutes, then allowed Oklahoma to creep back in it with a shaky start to the second half. Obi Muonelo kept the Sooners from completing the comeback, scoring 10 of his 15 points after the rally to send the seventh-seeded Cowboys into Thursday's quarterfinals against ninth-ranked Kansas State, the No. 2 seed. Oklahoma (13-18), seeded 10th, played without leading scorer Willie Warren (ankle) and will miss the postseason a year after reaching the NCAA regional finals. The Sooners closed out a disappointing year filled with injuries, suspensions and inconsistency with a nine-game losing streak, their longest since dropping 10 in a row in 1963-64. Tommy Mason-Griffin had 22 points and nine assists, and Steven Pledger added 18 points for Oklahoma. The third Bedlam game came after a split in the regular season. Oklahoma won in overtime at home with the Big 12 player of the year, OSU's James Anderson, on the bench for most of the second half with a head injury. With Anderson back, the Cowboys won by 21 in the second meeting in Stillwater. Bedlam III looked like a blowout at the beginning. Muonelo opened the game with a 3-pointer from the top of the key, and Page followed with two more to make it 9-0. Oklahoma State kept hitting, Oklahoma kept missing, and the Cowboys were quickly up 20-2, an opening blitz capped by Page's third basket from beyond the arc. Page hit two more 3-pointers in the half, including a contested one from 30 feet that hit the front of the rim and tumbled over, and Oklahoma State made 17 of 29 shots to lead 45-23. But, this being Bedlam, it wasn't over. Not yet. Oklahoma tightened defensively, found its rhythm offensively and opened the second half with an 11-0 run. Oklahoma State didn't score in the first 4:44 of the half as the Sooners hit seven of their first nine shots, cutting what seemed like an insurmountable lead to 45-34. Muonelo ended Oklahoma's hopes. The senior guard scored eight points in a two-minute span, then hit another jumper and added a pass to a cutting Matt Pilgrim for a layup that put the Cowboys up 65-47. Oklahoma never got closer.