Gor went into the clash without a number of key players, including Nicholas Kipkirui and Kenneth Muguna.
The home side had a blistering start to the match, breaking the deadlock through Amir Sayoud within just seven minutes of gameplay after he caught the goalkeeper Gad Mathews off his line with a brilliant free-kick.
Hamza Bellahouel doubled the advantage seven minutes later, before Sayoud making it 3-0 in the 20th minute from the penalty spot after Koukpo was fouled in the area.
Koukpo nearly made it 4-0 in the 27th minute but his shot inside the box missed the target by inches.
Larbi Tabti went on to score the hosts fourth minutes to the break after a defensive gaffe that allowed him space to shoot.
The restart of the match saw CR Belouizdad pick from where they left, with Sayoud completing his hat-trick of the night in the 51st minute.
Ngombo, who came on as a substitute got his name on the scoresheet for his side’s sixth goal in the 67th minute as the tie ended 6-0. Gor Mahia now face a daunting task of overturning the scoreline when they host Belouizdad in Nairobi for the return leg on Sunday, January 3.
The aggregate winner between the two sides will earn a slot in the group stages of the continental showpiece.