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.
Maryland point guard Melo Trimble, considered a lock to leave the program before struggling in the second half last season, has withdrawn from the NBA draft and will return for his junior season.
Louisville's Chinanu Onuaku, who recently underwent a medical procedure to correct a heart rhythm issue detected during the combine, will keep his name in the NBA draft pool.
Andrew White III will return to the Nebraska men's basketball team next season after removing his name from the NBA draft.