Hamdi Fathi celebrates one of his two goals against US Monastir (Ahram)
Winger Ahmed Abdel-Kader needed quarter of an hour to put Ahly in front before Fathi's brace either side of the interval sent the Red Devils through as they continue their bid to win a record-extending 11th crown.
Ahly joined Zamalek in the group stage after their Cairo rivals crushed Burundi's Flambeau du Centre 5-1 for a 6-1 aggregate win in the Champions League second preliminary round on Friday.
Swiss coach Marcel Koller has now enjoyed two wins out of two since taking over last month as Ahly also defeated Monastir 1-0 away in the first leg.
At Cairo's Al-Salam Stadium, Monastir were repeatedly exposed on their right flank and Ahly punished them on 15 minutes to go ahead.
A threaded pass from left-back Ali Maaloul eluded Monastir's Omar Bouraoui and released Abdel-Kader, who fired a powerful shot into the far top corner from a narrow angle.
Algerian forward Abdelhakim Amokrane missed a golden chance to bring Monastir level on 30 minutes when a poor defensive clearance rebounded off another defender and fell to him to break clear but he blasted his shot high over with only the keeper to beat.
But Ahly ended the match as a contest two minutes before the break when Monastir keeper Bechir Ben Said grasped at thin air following a corner and Fathi headed home in off the post.
Amokrane again squandered a goal-scoring opportunity early in the second half when his free, far-post header missed the target but Ahly quickly re-assumed control.
Although Brazilian forward Bruno Savio, who joined from Bolivia's Club Bolivar in the close season, was a peripheral figure in a central playmaking role, Ahly were still efficient going forward.
Their set-pieces were vital against Monastir, with Fathi glancing a superb header home following a free-kick from winger Taher Mohamed Taher in the 57th minute.
Ahly wasted further chances to increase the gap and had a goal disallowed for offside in the latter stages but it mattered little as they strolled into the last 16.
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