Releford netted 12 points and Withey provided 11 with 10 rebounds in the defensive struggle as the Jayhawks (17-1, 5-0 Big 12) recorded their 16th consecutive win.
Ben McLemore also reached double figures with 11 points as Kansas bested its intrastate rival for the 45th time in 48 meetings.
Shane Southwell put in 19 points and hauled down seven rebounds for the Wildcats (15-3, 4-1), whose eight-game winning streak was snapped.
Angel Rodriguez supplied 12 points and eight assists for Kansas State.
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