Simmons made all four of his 3-point attempts as Ohio hit 11 of 20.
Ohio was held scoreless for the first four minutes of the second half until back-to-back 3-pointers gave the Bobcats a 41-39 lead. Simmons scored eight straight points to extend it to 57-48 and Ohio led by at least eight points the rest of the way.
Block and Campbell had 10 points apiece in the first half to help Ohio build a 35-31 lead.
Thomas Wilder led Western Michigan (7-11, 1-4) with 21 points, including 9-of-12 shooting from the stripe.
Western Michigan trailed 18-13 midway through the first half before going on a 14-0 run for a 27-18 lead.