Ten-man Ahly tasted their first defeat under Rene Weiler after slumping to a 1-0 loss to Tunisia's Etoile Sahel in their opening group stage game of the African Champions League in Rades, with Spanish coach Juan Garrido getting the better of his former employers.
Yassine Chikhaoui scored the winner early in the second half, capitalizing on a defensive lapse to sneak between three defenders and volley home a right-wing cross.
But Ahly will feel hard done by after central defender Ayman Ashraf received his marching orders after 13 minutes for a last-man foul on an Etoile forward, although television replays suggested that the straight red card was harsh.
When Ashraf committed the foul, the Etoile man was not in a certain-goal position as he anticipated a long ball.
With one man down, Ahly, who are eyeing their first Champions League title since winning the last of their record eight crowns in 2013, failed to mount any threats.
Garrido, who led Ahly to the Confederation Cup title in 2014, emerged winner from his first duel against the club since his departure, handing Swiss boss Weiler his first defeat at the helm in the process.
Ahly have enjoyed seven straight wins since Weiler took over in the summer, earning plaudits for a series of vivid attacking displays.
Etoile top Group B with three points, on level with Sudanese giants Al-Hilal, who beat Zimbabwe's FC Platinum 2-1 at home in the other group match.
Weiler stuck to his bold strategies despite playing away from home, fielding two attacking-minded holding midfielders as Ahly pushed forward from the outset.
However, the sudden dismissal of Ashraf took the wind out of their sails, forcing them to retreat in their own half as Weiler took off winger Walid Soliman to introduce a defender in Mohamed Hani.
Etoile struggled to make use of their numerical advantage in the first half though, creating only one chance in the 18th minute when Chikhaoui broke the offside trap to run onto a through ball and send a sliding effort over the crossbar.
But he made amends in the 50th minute in superb fashion, chesting a floated ball from Mohamed Methnani to volley home from eight yards out.
Both sides lost a key player to injury, with Ahly's Ali Maaloul and Etoile's Chikhaoui limping off in pain.
The closest Ahly came to finding the net was a tame far-post header from Nigerian forward Junior Ajayi that the keeper easily collected as Etoile held on for a precious win.
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