With Mercer (22-8, 13-4 Atlantic Sun) leading 69-66 and just 20 seconds to play, North Florida's Nesbitt was fouled on a layup and his three-point play tied the game at 69 forcing overtime.
Nesbitt's heroics continued into overtime on a tie-breaking layup with 38 seconds to play. Nesbitt scored again on a dunk following Mercer's missed 3-pointer and the Ospreys led 78-74 and held on for the win.
North Florida (15-15, 9-8) trailed Mercer 35-30 at the break but bounced back to a 41-39 lead after the first 7 minutes of the second period.
Langston Hall led Bear scorers with 24 points and Mercer still remains tied atop the conference as co-leader Florida Gulf Coast also lost on Thursday night.