The Eagles opened overtime on a 10-0 run. Terrell made a 3-pointer and two free throws during the stretch.
Marc Eddy Norelia scored 13 points and grabbed 11 rebounds for Florida Gulf Coast (5-4). Zach Johnson added 12 points with six assists.
Diaz had 19 points, nine rebounds, seven blocks and three steals to lead Florida International (4-5).
Daviyon Draper made a pair of free throws to give FIU a 71-67 lead with 1:41 left. Terrell answered with a jumper, and Demetris Morant had a dunk to tie it at 71 with seven seconds left to force overtime.