The two sides boast a proud tradition in Asian football, with nine continental titles and 18 appearances in the AFC Champions League knock-out stage between them. Nevertheless, Tuesday marks only the second time Al Ittihad and Al Hilal have met in the competition - the first being Al Ittihad's 3-1 win in the 2011 Round of 16.

With nine Continental trophies and 23 Saudi League titles between them, Al Hilal and Al Ittihad are Saudi Arabia’s most successful teams and two of Asia’s greatest sides, but only one of them will make it to the last four of the 2019 AFC Champions League.

Al Hilal have reached the semi-finals three times in the past five years, while time has not been kind to two-time AFC Champions League winners Al Ittihad, whose last semi-final appearance dates back to 2012 when they lost to city rivals Al Ahli.

Xavi’s men overcame rivals Al Duhail 1-0 in the Sheikh Jassim Cup, Qatar’s annual ‘Super Cup’ competition, just a week after they had eliminated the same side from the AFC Champions League Round of 16.

Meanwhile, Al Nassr walked away from Abu Dhabi with the quarter-final ticket after defeating Al Wahda 4-3 on aggregate.

Taking into account only figures from teams and players still involved in the Continental competition, we’ve hand-picked some of the stats and facts that have caught the eye.

Five former winners are aiming to lift the coveted trophy for the second or even third occasion, while three of the sides will look to create history and be crowned AFC Champions League winners for the first time.

Ahead of the four first legs, which take place between Monday and Wednesday, the-AFC.com has selected five things to look out for in a week that will see some of Asia's biggest club sides square off in a quartet of mouth-watering match-ups.

The quarter-finals were introduced in the AFC Champions League back in 2004, and since then we have witnessed some action-packed matches, particularly in recent times. the-AFC.com highlights five last eight ties that are worth reviewing and savouring.