Mahmoud hits treble
Brazilian striker Clemerson de Araujo and summer arrival Juninho also each scored twice as Al Gharafa maintained their 100 per cent start to the competition.
Mahmoud opened the scoring after just five minutes before Brazilian strike partner De Araujo doubled the lead two minutes later. Mahmoud and De Araujo increased the lead before Brazilian midfielder Juninho added a fifth with a 30th minute penalty. Al Gharafa continued their attacking display in the second half as Mirgani Al Zain netted just before the hour mark.
Mahmoud completed his hat-trick four minutes later before former Lyon midfielder Juninho sealed the win with his third goal in two games for his new club with 13 minutes remaining.
In Group B, Al Sadd beat second division Al Shahaniya 4-0. Talal Al Baloushi and Majed Mohamad handed Al Sadd a comfortable lead after just 20 minutes before Ali Abdulwahab was sent off for Al Shahaniya just after the hour mark.
Ali Afif added a third for Al Sadd with a minute remaining before Ghanaian striker Agyeman Opoku sealed the win in the second minute of stoppage-time.
In other matches, Al Arabi shared a scoreless draw with Al Khraitiyat, while Al Siliya beat Al Wakra 2-0.