Mercer (15-9, 8-3 Atlantic Sun Conference) has won 12 straight at home in Hawkins Arena.
After Kordario Fleming's layup gave Jacksonville the lead 58-57 with 8 seconds left, Hall went one of two from the foul line to send the game into overtime.
Tied 62-62 in overtime, Hall's layup put the Bears ahead 64-62 with 1:54 left, but Javon Dawson answered with two free throws to tie it again 64-all.
After a turnover by Jacksonville's Russell Powell, Smith made a 3-pointer with 30 seconds left to put the Bears on top 67-64. Dawson missed a 3-pointer with 3 seconds.
Jarvis Haywood led Jacksonville (12-13, 7-5) with 13 points and Fleming added a double-double, 10 points and 11 boards.
SMU has signed a second player from Australia, 6-foot-11 forward Harry Froling, to a national letter of intent. The Mustangs previously signed guard Tom Wilson from Australia.
There's nothing to suggest the Jayhawks won't end up atop the Big 12 for a 13th season in a row. But what about a return to the Final Four?
Colorado State graduate transfer John Gillon has chosen Syracuse, giving the Orange a potential starter at point guard entering the 2016-17 season.