The Eagles (10-3, 3-1 Sun Belt) trailed 34-31 at halftime, but Hewitt drained back-to-back 3-pointers as Georgia Southern opened the second half on an 11-2 run, claiming a 42-36 lead.
South Alabama (4-11, 2-3) fought back with a 12-5 run of its own briefly regaining the lead.
The Eagles' Mike Hughes made back-to-back steals - one leading to a Curtis Diamond 3-pointer and the other a Hughes layup - as part of a pivotal 11-3 run that pushed the lead to 70-61 inside four minutes. South Alabama didn't get closer than eight after that.
Ken Williams led the Jaguars with 23 points and three others scored 10 each.
Hughes had three of Georgia Southern's eight steals as the Panthers scored 25 points off turnovers.