The Sooners were only a measly 28.6 percent in the first half.
"Withey does a terrific job and I thought he kind of set the tone early in the ballgame," said OU head coach Lon Kruger. "We just never did get any flow offensively."
Meanwhile, KU wasn't that much more efficient, but it was plenty enough with its 43.6 percent from the floor despite committing 14 turnovers.
And they dominated the boards, capturing that battle 41-31.
Simply put, the Jayhawks just outmuscled OU in a game that proved to be ugly from the beginning.
Even with how poorly their execution was offensively, though, the Sooners still hung around.
But trailing by eight or 10 most of the way, they couldn't get that shot to get them over the hump.
"It was a ballgame where we were trying to hang in there most of the way and just couldn't quite ever get to a point where we threatened seriously down the stretch," Kruger said."
OU didn't have enough firepower to storm back into it after that.
The Sooners led early on 5-2, but a Romero Osby missed dunk allowed the Jayhawks to seize the momentum and regain that short lived lead.
Speaking of Osby, the senior forward just couldn't get going all day, and Withey certainly had a lot to do with that.
OU's most productive player, Osby finished with just 12 points on 4-for-16 shooting.
"He's definitely a good shot-blocker, but [my play] is on my part," Osby said. "I could have done a better job just making shots, and it's the first time I've played against a 7-footer. It's the first time I've played against a shot-blocker as good as he is. I've got to take responsibility for the shots I usually make."
McLemore, who led all scorers, paced KU with his 18 points on 5-of-10 shooting.
Withey posted about as complete of a game anyone has on OU in a long time, pouring in 13 points to go around nine rebounds, four blocks, three steals and an assist in 34 minutes.
"Jeff played great," said Kansas coach Bill Self. "He made some plays that I think would rival some of the better plays that he's made this entire year."
Guard Travis Releford finished as the third Jayhawk in double figures with his 10.
Osby and forward Amath M'Baye each had 12 for the Sooners, and guard Steven Pledger added 10.
KU led 29-21 at intermission despite points in the paint being an even 10-10 fight.
The Jayhawks opened that up in the second half, eventually outscoring the Sooners 28-16 inside.
OU (13-5, 4-2 Big 12) will now try to regroup in time for a 7 p.m. CT Wednesday game in Waco, Texas, against the Baylor Bears.