The defeat continues Al Hilal's poor away form in the tournament but they will be confident of overturning the slender deficit in Saudi Arabia on October 20.

The hosts were the livelier of the two sides in the first half with Brazilian striker Igor Castro and Iran international Mohammad Reza Khalatbari proving particularly dangerous.

Al Hilal goalkeeper Hasan Al Otaibi had to be alert to deny a close-range header from Castro before his low shot in the 23rd minute was cleared by Osama Hawsawi.

Right-back Mohammad Hoseini shinned a corner narrowly wide on the half hour as Zob Ahan continued to press.

Al Hilal had been largely quiet in the first half but had a golden chance to snatch the lead four minutes before the break.

Saudi Arabia striker Yasser Al Qahtani was brought down in the area by Mohammad Ali Ahmadi as he was about to attempt a lob over the onrushing Shahab Gordan, but Swedish veteran Christian Wilhelmsson fired the penalty straight at the goalkeeper.

It proved a costly miss as Zob Ahan took the lead 12 minutes into the second half when Hadadifar hit a low free-kick which went through a gap in the Al Hilal wall created when Wilhelmsson turned away and the ball flew past an unsighted Al Otaibi.

Determined to try to snatch a crucial away goal, Al Hilal went on the attack in the closing stages and Nawaf Alabid struck the woodwork in the 70th minute.

The midfielder almost snatched a draw in injury time when he tried to connect with a superb Ahmed Al Fraidi cross but Hoseini somehow managed to put him off and the chance passed.