In Group A, Zob Ahan of Iran was held to a goalless draw by Al Zawraa of Iraq in Isfahan.
On Monday, Alireza Mansourian’s side will play Al Nassr of Saudi Arabia at the Al Maktoum Stadium in Dubai, the UAE, while Al Zawraa will host Al Wasl of the UAE.
In Group C, Al Duhail of Qatar emerged 3-0 triumphant against fellow 2018 quarter-finalist Esteghlal and Al Hilal came away with the three points from Al Ain following a 1-0 victory at Hazza bin Zayed Stadium in matchday one.
The two winners from the opening round of games clash at King Saudi University Stadium in Riyadh with the winner taking early strides towards qualification to the knock-out stage.
Meanwhile, Al Ain will travel to Tehran to face Esteghlal on Tuesday on the back of a poor run of form that saw them win just one of their last four games in all competitions. The UAE side is without suspended captain Ismail Ahmed who was sent-off in the previous match.
Tuesday sees a repeat of the 2018 semi-final as Al Sadd hosts Persepolis in Group D. The Iranian side had won 1-0 in Doha and went on to reach the final following a 1-1 draw in the return leg.
This time around, both teams go into the fixture on the back of disappointing results; Al Sadd was beaten 2-0 by Saudi Arabia's Al Ahli in matchday one, while Persepolis could only muster a 1-1 draw at home against Uzbekistan's Pakhtakor.
Al Ahli's most recent trip to Uzbekistan ended in disappointment when they lost 2-1 to FC Nasaf in 2016. Pakhtakor, meanwhile, have not lost at home in the AFC Champions League since 2013.