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.
Former Kentucky guard Ed Davender, the only Wildcat with at least 1,500 points and 400 assists, has died. He was 49.
Guard Naz Mitrou-Long, whose 2015-16 season ended in December due to hip problems, has been granted a hardship waiver for the coming season, Iowa State said.
As the Sooners look to life without superstar Buddy Hield and his sidekicks, it's clear their unseasoned players will need to grow up fast.