كتب : وكالات
A first-half strike by in-form forward Mohamed Farouk meant that Ahli conceded for the first time in five games.
Youngster Amr Gamal equalized for the Reds though, but a red card to captain Wael Gomaa forced a penalty that was converted successfully by Mohamed Adel.
Despite the defeat, Ahli remained in charge of Group A with 12 points from five games,while Contractors moved to third.
It is the first time for Contractors to beat Egypt's record champions Ahli in the league since 1996.
VIDEO HIGHLGHTS
Farouk opener for Contractors.
Gamal equalizes with a fine finish for Ahli.
Penalty and red card incident followed by Adel winner from the spot.