كتب : Hatem Maher
Masoud Shojaei put the hosts ahead 12 minutes after the break when his right-footed shot from the edge of the area went past the keeper.
Naif Hazizi drew Saudi Arabia level in the 79th minute when he latched onto a deft through pass to slot home.
Central defender Osama Al-Harbi gave the Saudis all three points three minutes from time.
He towered above his marker to head home a right-wing corner and hand his side a precious win.
Saudi Arabia moved into third spot in Group B with seven points, one behind second-placed Korea Republic.
The Asian powerhouses have a chance to book one of the top two spots in their group and earn an automatic qualification for the World Cup.
If they finish third, they will play off against Group A's third-placed team and the winner will take on Oceania champions New Zealand for the final place in the 32-team tournament.
Iran's Goal
Saudi Arabia's equalizer
Saudi Arabia's winner