Ellis led all scorers with 28 points and had 12 rebounds. Florence chipped in 27 points.
Daniel Emerson also had a double-double for the Bears (15-11, 9-6 Atlantic Sun Conference), scoring 13 points and pulling down 15 rebounds.
Garfield Blair led four Stetson (13-12, 9-7) players in double figures with 24 points and a career-high 16 rebounds. Tim Lang added 18 points and 10 rebounds, while Eric Diaz added 12 points and Kris Thomas chipped in 10 points.
Mercer trailed by as many as 18 points, 56-38, with 13:56 left in regulation. The Bears went on a 31-11 run capped by a three-point play by Ellis for a 69-67 Mercer lead with 41 seconds left in regulation.
Stetson tied the game at 69-69 on two free throws by Blair.