Defending champions Ahly are second in the Group B standings
Sudan's Al Hilal routed holders Ahly 3-0 and climbed to the top of the Champions
League Group B standings on Sunday.
Al Hilal handed the Egyptians their heaviest defeat in the competition for 30 years to throw the race for semi-final places wide open.
Both sides have nine points from five matches with one more round of games to play.
The Ivory Coast's Asec Mimosas stayed in contention for a last four berth by beating Tunisia's Esperance 2-0.
Following the win in Abidjan, Asec have seven points while Esperance were eliminated as they only have four points.
Mozambican defender Dario Khan opened the scoring for Al Hilal with a powerful header from a corner just before the hour mark, rising above Ahly's keeper Essam Al Hadari.
The second followed 12 minutes later in more spectacular fashion as substitute Hassan Isaac Korongo hit a stunning long range shot from midway inside the Ahly half along the ground and past Al Hadari.
The rout was completed three minutes from the end by Al Hilal's Nigerian import Ndubuisi Eze, who squeezed past two defenders and slotted the ball wide of the goalkeeper.
Ahly last lost 3-0 in 1977 when they were beaten in the quarter-finals of the old-format Champions Cup by Hearts of Oak of Ghana.
Sunday's loss was the second successive defeat in the group for the Egyptians, although they need just a draw at home to Asec in their last game on 2 September to qualify for the semis.
Ahly are chasing an unprecedented third successive Champions League victory.
Asec took an hour to break the deadlock before Ghana import Idrissu Abdul Nafiu set up the opening goal.
The shot was initially saved by Esperance goalkeeper Hamdi Kasraoui but
bounced into the net off the back of Esperance's new centre back Bilel Yaken.
Ali Diarra made sure of the three points 12 minutes later with a powerful header as he stole in late and unmarked into the Esperance penalty area.