Jerron Granberry scored a game-high 23 points to lead UNF (14-18), with 16 coming in the second half to lead the comeback as the Ospreys rallied from a 10-point deficit in the final 11 minutes.
The comeback overshadowed a double-double from Ayron Hardy, who led JU (19-11) with 12 points and 10 rebounds.
In a foul marred contest, UNF won the game at the free throw line, hitting 23-of-35 at the stripe while JU hit 20-of-31. The two teams combined for 52 fouls, with 36 coming in the second half, with JU being whistled for 19 of those.
Jacksonville opened the second half with a six-point lead and pushed it to 10, 44-34, on a Travis Cohn layup with 11:17 left.
UNF got back-to-back 3-pointers from Parker Smith and Granberry, capping an 8-0 spurt with an Andy Diaz layup with 7:13 left to make it 50-49.
It looked like JU was going to survive when they got the lead to six, but a controversial technical foul called on Hardy gave UNF two free throws and the ball, starting a four-point possession that changed the game.
UNF tied the game for the first time in the second half at 59 with 3:50 left, took its first lead on the next possession on Diaz jumper and pushed the lead to five, 65-60 on a Jimmy Williams free throws with 19 seconds left.
The Dolphins looked for a miracle and almost got it when Keith McDougald drained a three in the corner and was fouled, cutting the deficit to one, 65-64, with eight second left.
Granberry stroked a couple of free throws to push the lead back to three and fouled JU before getting off a game-tying three. Aloys Cabell missed the first free throws and had to intentionally miss the second, with UNF getting the rebounds and sealing the win.
UNF got 19 points and seven boards from Diaz with Williams adding 12 points and nine boards. JU got 10 points from Delwan Graham.
JU shook off a slow start to take a 28-22 lead at halftime, with seven different Dolphins scoring in the first half.
The loss ends the Dolphins season at 19-11, just one win shy from a second straight 20-win season.