Ahmed Akaichi gave the hosts a third-minute lead in Mediterranean resort Sousse from an offside position, slamming a rebound into the net from point-blank range.
A low cross eluded several defenders and Abdessalam Benjelloun tapped the ball over the line to silence a near-capacity crowd at the 25,000-seat Stade Olympique.
Moroccan clubs occupy the prime positions in the standings with a 2-1 away win over Al Ahly Tripoli of Libya giving Kawkab Marrakech a maximum six points after two rounds.
FUS have four points, Etoile one and Ahly, handicapped by having to play home matches in Tunisia because of the Libyan security situation, appear out of contention following two losses.
TP Mazembe of the Democratic Republic of Congo top Group A with six points, Mouloudia Bejaia of Algeria have four, Medeama of Ghana one and Young Africans of Tanzania are pointless.
A Merveille Bope goal gave Mazembe a 1-0 win at Young Africans while woeful finishing by hosts Medeama enabled Bejaia to escape with a 0-0 draw.
Matchday 3 fixtures are scheduled for mid-July.