When the AFC Champions League was inaugurated in 2002-03, Al Sadd and Al Hilal became the maiden representatives of their respective countries in the competition.

Both sides had already been continental champions, with Al Sadd lifting the Asian Club Championship trophy in 1989 and Al Hilal following suit three years later before adding a second title in 1999-2000.

The two-legged fixtures will kick off on Tuesday and Wednesday with the return legs three weeks later. The two winning sides will progress to the final to be played on November 11 and 24.

We look at four players – one from each of the semi-finalists – who could be key for their respective teams' chances of victory.

Last minute winners, goal gluts and East-meet-West clashes, since the AFC Champions League's revamp in 2002-03, there have been plenty of thrills and spills when the tournament has reached the final four phase.

The-AFC.com looks back on some of these ties to remember and relive.

Although clubs from Saudi Arabia and Qatar have appeared in every single edition of the AFC Champions League since its inception in 2002-03, they managed to avoid facing-off in the knockout stages until 2009, but in the decade since, they have been pitted together on 10 occasions. The-AFC.com looks back at how each of these encounters panned out.

Wins were exchanged when the two sides met in the group stage of the 2015 edition, with Khalfan Ibrahim’s strike giving Al Sadd a 1-0 home win on Matchday Two and Al Hilal emerging 2-1 winners in Riyadh on Matchday Six; the last time the two sides met. the-AFC.com tracks where all 22 starting players involved in that last encounter are now.

Despite going one down within the first 10 minutes, goals from Andre Carrillo, Salem Al Dawsari and Sebastian Giovinco helped Al Hilal claim the victory which sent them through to the last four of the competition for the fifth time in the club’s history.

With their fans roaring them on at the Jassim bin Hamad Stadium on Monday, the Qatar champions overturned a 2-1 first leg deficit to beat Saudi Arabia's Al Nassr 3-1 to advance to the semi-finals 4-3 on aggregate.