They fell behind 4-0 early, but tied it at six on a lay-up by Jasmine Wynne with 14:50 left in the first half. The Bulls grabbed and held the lead thereafter, despite shooting just 34.3% from the field in the first half.
USF carried a 36-22 lead into the locker room.
The closest FIU would come was when they cut the deficit to ten with 4:45 remaining. Jerica Coley hit a free throw shot to make it 66-56 USF.
The Bulls took 17 attempts from beyond the arc in the first half, sinking just three of them. After the break, the Bulls changed up their game plan, pounding out 20 points in the paint in the second half while taking just five attempts from three-point range.
"We talked about that," Fernandez said of his team in the first half, "I thought we settled for jump shots, we settled for perimeter shots."
The Bulls struggled with fouls, leading to 23 points for FIU from the charity strip. Tiffany Conner fouled out, while Kaneisha Saunders and Akila McDonald each had four.
Despite the foul trouble, McDonald posted a career-high 12 rebounds along with eight points in just 16 minutes on the floor. Wynne and Andrell Smith paced the Bulls with 15 points apiece.
For the Panthers, Coley delivered a dominant performance of 30 points, 14 rebounds, and five assists. It was the eighth game this season of 30 points or more for the Sun Belt Conference Player of the Year.
With Saturday's victory, the Bulls stay alive in the WNIT and advanced to the third round, where they will take on the winner of the Wake Forest-James Madison match-up.