Thomas grabbed nine rebounds and Lenzelle Smith Jr. finished with 14 points as the Buckeyes (9-1) broke open a close game in the second half and logged their fifth straight win.
Aaron Craft helped Ohio State overcome an anemic 38.6 percent shooting mark with five assists.
Winthrop (4-5) lost despite good performances from Derrick Henry (12 points) and Joab Jerome (eight points, 10 rebounds).
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