The visitors tool the lead in the 19th minute of the match through Maher Hannachi.
The Tunisians got the second goal in the 69th minute through Mohamed Msakni, who converted a penalty awarded to his side when a Tunisian player was brought down inside the 18-yard box.
Speaking after the match, the coach of Rangers International, Olugbenga Ogunbote, blamed the defeat on injuries suffered by his players.
He, however, expressed the hope that his players will play better in their next match against CS Sfaxien and Salitas of Burkina Faso.