Thomas connected on 10-of-12 foul shots and hauled down seven rebounds to provide a spark for the Buckeyes (18-6, 8-4 Big Ten), who snapped a two-game losing streak.
Amir Williams came off the bench to help out with 10 points and eight rebounds in the win.
The Wildcats (13-12, 4-8) were led by Tre Demps with 16 points.
Kale Abrahamson added 13 and Reggie Hearn donated 12 for Northwestern.
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