McDermott netted 24 of his total in the first half as the Bluejays (15-2, 5-0 Big East) posted a 53-24 lead after 20 minutes and never looked back.
Austin Chatman added 10 points for the winners.
Butler (10-7, 0-5) was led by Kellen Dunham with 12 points.
Khyle Marshall provided 11 for the Bulldogs.
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