كتب : Sherif Tarek
Malek Mouath netted the opener for Ahli late in the first half, and nearly ten minutes after restart Sultan Al-Numare scored the leveler.
Seven minutes from the final whistle, Hassan Al-Raheb shocked the Dean by hitting the winner.
On slumping to a defeat, Ittihad moved back to second place with 40 points, while defending champions Hilal have become leaders on goal difference.
On the other hand, Ahli now lie fifth with 25 points, trailing fourth-placed Ettifaq by one point.
Lackluster Performance
Striker Emad Meteb was included in Ittihad's starting eleven, but his lackluster performance prompted coach Gabriel Calderon to substitute him on 70 minutes.
The Egyptian international, who seemed upset when he was on his way to the dugout, squandered a golden opportunity to score 13 minutes after the interval.
He went one-on-one with the keeper, but his drive drifted wide of the mark.
However, Meteb is not solely responsible for his team's first loss, as Ittihad were outnumbered for about half an hour after defender Reda Tukar received his marching order two minutes after the hour mark.
Ahli's Egyptian newcomer Walid Soliman didn't feature in the pivotal game.
He's set to take part in the first training session with his new team on Monday.
The 25-year-old playmaker has just joined the Jeddah-based side from Egypt's Petrojet on a six-month loan deal.