Al Ahli Saudi recovered from a goal behind to draw 1-1 with Al Ahli of the UAE thanks to a strike seven minutes before halftime by Abdulfattah Asiri in their first leg.
In Tehran, Al Ain -- finalists last year and champions in 2003 -- struggled without their Saudi Arabia international Nasser Al Shamrani in a game of few chances.
The 33-year-old forward had to stay behind in the UAE after being unable to gain entry to Iran due to a diplomatic impasse between the Saudis and Iranians.
Asian Player of the Year Omar Abdulrahman failed to inspire his Al Ain team and the best chances of the game fell to Esteghlal's ineffective Esmaeili until Rezaei scored from the spot in added time after Lee Myung-joo's handball in the area.
In Jeddah, Khamis Esmaeel put the Dubai club ahead in the 21st minute after the hosts failed to clear Everton Ribiero's free kick into the area but Asiri levelled with a precise shot to leave the tie finely poised ahead of next week's second leg.
(Reporting by Michael Church in Hong Kong; editing by Ken Ferris)
