El Jaish needed to raise their game a few notches to overcome a two-goal deficit following their 3-1 defeat in the first leg, but despite Brazilian Romarinho's double the Emirati giants held their nerve to clinch a last-gasp draw with Mohamed Abdulrahman finding the net in the fifth minute of stoppage time.
Al Ain, the champions in 2003 and the runners-up in 2005, will in all likelihood take on South Korea's Jeonbuk Motors in the final as they hold a massive 4-1 advantage over Seoul ahead of their semi-final second leg match on Wednesday.
Following a goalless first half which saw both teams miss several chances, Omar Abdulrahman put the Emiratis ahead in the 57th minute with a low shot into the bottom left corner of the net after combining with Brazilian Ciao to split the El Jaish defence with an exchange of precision passes.
El Jaish, however, equalised 10 minutes later when ex-Barcelona star Seydou Keita found Romarinho and the diminutive midfielder's shot from the edge of the area found the net after taking a deflection off Ismail Ahmed.
Romarinho, who has modeled himself on his idol, the Brazilian legend Romario, then put El Jaish ahead almost in similar fashion, with Keita providing him with the vital assist yet again in the 81st minute.
Things then got desperate as Ciao went close in the 84th minute and Mohamed Abdulrahman saw his header blocked by El Jaish goalie Khalifa Ababacar.
With three minutes remaining, Al Ain's Mohammed Fayez threw himself down to thwart Sardor Rashidov's strike from the right and Ciao also missed another chance to register his name on the score sheet.
However, Mohamed Abdulrahman found the net more than four minutes into stoppage time to put Al Ain on course for a possible second continental title.