كتب : Hatem Maher
Issam Merdassi scored the winner just before the break to snap Ahli's unbeaten run and give Sfaxien their first victory in the group stage.
The result put Sfaxien on top of Group A with three points while Ahli, who are yet to open their account, were left fourth with no points.
JS Kabylie play Asante Kotoko on Sunday the group's second tie.
Sfaxien dominated the midfield in first-half, launching several attacks on the title holders' goal, while Ahli lacked both the defensive toughness and the attacking approach.
The African Champions failed to penetrate through the flanks with Islam Al-Shater and new-signing Tarek Al-Saied struggling to find their form.
Playmaker Mohamed Abou-Treika tried to nudge the Tunisians from the midfield but he never found support from holding midfielders Mohamed Shawki and Hassan Mostafa.
Egypt striker Emad Meteb and Angola's World Cup goal-scorer Flavio Amado looked rusty and the latter was changed in the end of the first-half after collecting a thigh injury.
Striker Blaise Koissy had the first opportunity for Sfaxien in the 13th minute when he latched on to a neat pass before steering a close-range drive just wide.
Shortly after, Anis Boujelbene nipped between Ahli's stoppers Wael Gomaa and Emad Al-Nahhas but international keeper Essam Al-Hadari stretched to block his low shot.
The hosts, backed by huge and enthusiastic crowd, continued their attacking waves and Shuaibu Ishola almost opened the score line with a powerful drive from the edge of the area that went over the bar.
Merdassi finally broke the deadlock in the 45th minute after he connected with Aymen BenAmor inch-perfect cross and headed past Al-Hadari.
Ahli's only chance throughout the game came in the 67th minute when Mostafa's pass released Meteb inside the are but he fired the ball away from the goal.