McLemore went 5-of-6 from 3-point range while Jeff Withey added 14 points and 10 rebounds for the Jayhawks (25-4, 13-3 Big 12).
Elijah Johnson contributed a double-double of 12 points and 10 assists as Kansas notched a sixth straight win.
The Jayhawks came into the contest tied with Kansas State for the top spot in the Big 12 Conference standings.
The Mountaineers (13-16, 6-10) were led by Terry Henderson with 20 points.
Dominique Rutledge compiled 17 with 13 rebounds in the loss.