Al Ain will face another Saudi side in the last four after Al-Hilal edged Qataris Al Sadd 1-0 on aggregate in their quarter-final after a goalless draw in Doha.
With Gyan in sparkling form, Al Ain do not have to worry about where the goals will come from.
The Ghanaian has amassed his dozen in 10 games, with Al Ittihad the only side to keep him out in the duo's 1-1 draw in group play back in April.
However, the Saudis were unable to call on their supporters in Tuesday's clash after the AFC banned home supporters from attending the match in Mecca following unruly fan behaviour in the previous round.
Undeterred, the 2004 and 2005 winners grabbed a 35th-minute lead against the run of play at the King Abdulaziz Sport City after Ismail Ahmed turned into his own net following a neat turn and cross by Brazilian Marquinho down the right.
The visitors were back level only five minutes later though when Miroslav Stoch's lofted, curled pass found Gyan who swiftly controlled and dispatched after beating the offside trap.
Ittihad then needed three goals to advance and they poured forward in the second period but left huge gaps at the back.
A big punt forward from goalkeeper Khalid Eisa found playmaker Omar Abdulrahman in acres of space and the afro haired attacker cooly ran through and slotted home a second in the 65th minute.
Substitute Ibrahim Diaky added a third with eight minutes remaining after more good work from Slovakian Stoch, on loan from Turkish side Fenerbahce.
"We are satisfied with the performance and the result and we were relaxed after we scored the equaliser," Al Ain's Croatian coach Zlatko Dalic told reporters.
"We achieved what we wanted early in the match as this made things easier for the players and they were released from pressure and they showed a good performance.
"We are happy that we managed to repeat our victory today and to advance to the semi-finals."
- Sports & Recreation
- Al Ain
- Al Sadd