The 2003 winner took a 3-1 advantage to the Abdullah bin Khalifa Stadium on Wednesday (AEDT) and, after a goalless first half, their hero of the opening leg, Omar Abdulrahman exchanged passes with Caio to open the scoring before the hour.
That stirred El Jaish belatedly into life, with Romarinho levelling on the night midway through the second period.
The Brazilian then picked out the bottom corner with nine minutes remaining to set up a grandstand finish, where another El Jaish goal would have heralded a period of extra time that once seemed improbable.
But it did not come to pass, as Zlatko Dalic's men retained their threat on the break and, despite missing an earlier chance, Abdulrahman's brother Mohammed finished from close range to seal the club's final berth.
One of Korean duo Jeonbuk Hyundai Motors or FC Seoul lie in wait.