Ismaily lost further ground in their bid to win the league title after the struggling Arab Contractors defeated them 2-0 at home on Wednesday.
A few days after being held to a goalless draw by Ittihad of Alexandria in Ismailya on Saturday, the Dervishes slumped to their second defeat this season, squandering a golden chance to regain the league summit from leaders Ahly.
Ismaily are second on the league table with 41 points, just one point behind leaders Ahly, who have two matches in hand.
Youth striker Taher Mohamed Taher opened the scoring for the hosts in the 36th minute of the game, while defender Mohamed Samir doubled the seal two minutes after the break.
The Dervishes seemed harmed by the sudden departure of French coach Sebastien Desabre last month after being named as Uganda's new coach.
They played three games under the guidance of new coach Abou Taleb El-Issawi, claiming only one win over minnows El-Nasr before drawing with Ittihad of Alexandria.
Ismaily won the last of their three league titles in 2002.