Wholesale changes from Mosimane saw Ali Lotfi in goal and rare starts for Walid Soliman, Gerlado, Mahmoud Kahraba, Mahmoud Wahid and Aliou Badji.
Ahly hit the front in the opening seconds when Soliman made a forward run towards a looping ball before applying a cool, calm and composed finish in the six-yard area.
Gaish' fortunes turned for the worse in the 11th minute after fullback Ahmed Abdel-Rahman experienced an issue and was replaced by Ahmed Kabouria Mousa.
Angolan-born Gerlado, who was given his first start under Mosimane, extended the visitors tally two minutes towards the midway stage with a delicate chip from a through ball on the right-side.
Ahly worsened the home side's woes in the last seven minutes to halftime when Kahraba played a combination with Mohamed Fakhri for a superb finish.
Mosimane in conjunction with his assistant coach Cavin Johnson opted against refreshing the side with substitutions at the start of the second half, keeping the initial eleven.
With the game under control, Ahly still probed for more goals as the second half went by minute by minute with the hosts battling to get going on all fronts.
Saleh Gomaa and Ahmed El Sheikh entered on the side of the Cairo Red Devils in the closing minutes, as Mosimane looked to shut shop.
In the end, Ahly did enough to finish their domestic campaign on a winning note with the CAF Champions League final set for next month their next assignment.
