McLemore hit a layup and made two free throws on the next trip down the court during a 7-0 run that put the Jayhawks ahead 55-46 with 7:33 left.
West Virginia never recovered.
Kansas held West Virginia without a field goal over the game's first 7 minutes. Withey, who had a 25-pound weight disadvantage to West Virginia's Deniz Kilicli, scored eight of Kansas' first 14 points and he reached double figures midway through the half.
The Jayhawks twice built a 15-point lead before getting sloppy, and West Virginia trimmed the deficit to 38-30 at halftime.