The Red Devils thus surpassed the record of three Super Cup triumphs also achieved by bitter city rivals, Zamalek.
Flavio first found the target two minutes into the second half with a near-post header after he was set up by compatriot Gilberto.
Ivorian striker Kouassi Blaise drew Sfaxien level just after the hour mark before Flavio made the difference when he again connected home with a header a cross from Gilberto with 20 minutes left to play.
Without influential playmaker Mohamed Aboutrika, who was nursing a knee injury, veteran midfielders Ahmed Hassan and Mohamed Barakat did very little to assist lone striker Flavio.
Sfaxien were resolute in defence but Ahly could have still gone ahead in the first period after 18 minutes only to be denied by a superb save from the Tunisians' goalkeeper, Jassem Khaloufi.
Samm Audu, Goal.com