The Cameroonian champions reached last season's semi-finals before being eliminated on penalties by eventual winners Al-Ahly.
However, they were beaten in the first leg of their second qualifying round tie for this year's competition by their Algerian counterparts Setif on Sunday.
An El Hedi Belameiri strike in first-half injury time was enough for the hosts, who will take a slender advantage to Garoua for next weekend's second leg.
However, Mbwana Samata pulled what could be a crucial away goal back with just a minute left to play, meaning the tie remains in the balance ahead of Friday's second leg.
South African champions Kaizer Chiefs' hopes of qualifying for the tournament proper appear all but over after they were beaten 3-0 at Vita Club, with Firmin Ndombe notching a hat-trick at Stade Tata Raphael to put his side firmly in control.
Elsewhere in Sunday's Champions League action, Congolese outfit Leopards de Dolisie were held 1-1 by Al Hilal Omdurman, while CS Sfaxien grabbed a 1-0 win at Horoya courtesy of Fakhreddine Ben Youssef's strike on the hour.
