Two first-half goals from Emad Al-Nahhas and Flavio Amado secured the points of the game to make it 30 points from 12 games for Ahli.
This is while Petrojet conceded their third defeat in a row and are stuck in third spot with 25 points.
The Red Devils had a storming start putting a lot of pressure on the visitors' defense who were finally beaten by a 24th minute header from Al-Nahhas who rose high to convert Gilberto's cross in the back of the net.
And less than 60 seconds later, Angolan striker Flavio, whose header was denied by the woodwork at the beginning of the game, doubled the lead with an excellent chip ball from outside the area.
Ahli had at least a couple of chances to extend the gap but Mohamed Abou Treika and Ahmed Belal weren't harsh on Petrojet's defenders who made some terrible mistakes during the game.
The game was practically dead and the other 45 minutes didn't include any entertainment to end the game on a 2-0 win.