With all five groups underway, who has gotten the the best start in the ACL East Zone?

AFC Champions League debutants Viettel FC put in a spirited display against reigning champions Ulsan Hyundai but ultimately fell to a 91st-minute goal on Saturday evening. Chalinee Thirasupa / Power Sport Images

Action in all five groups in the East Zone of the 2021 AFC Champions League is now well and truly underway after the conclusion of Match Day 1 in Groups F and I on Saturday.

The expanded tournament sees the participation of a record nine clubs from Southeast Asia in the group stage this season, and they are set to fight for a berth in the Round of 16 by placing at least among the top two in their groups during the next couple of weeks.

While Malaysian Super League champions Johor Darul Ta'zim and Thai League 1 winners BG Pathum United look like ASEAN's best bets for a knockout berth after the opening engagements, the likes of Port and Chiangrai United could also turn things around in the coming days.

It might still be early days in the competition for the 20 clubs from the region, but here's what we have learned from action in East Asia following the opening set of fixtures.

Thai champions BG Pathum United off the mark in style

It has been a meteoric rise for BG Pathum United in Thai football as they lifted the Thai League title last season on the first attempt after returning to the top division. And it looks like they are already set to make an impact at the very top of the Asian football in the Champions League.

The ACL newcomers kicked off their continental campaign in Group F with an impressive 4-1 win over Philippines' Kaya FC-Iloilo, as both their hitmen Diogo and Teerasil Dangda struck twice at the Leo Stadium in Pathum Thani on Saturday.

It was an important win for Aurelio Vidmar's side as they got valuable points on board their upcoming clash against reigning Asian champions Ulsan Hyundai on Tuesday. However, it could be games against their ASEAN rivals Kaya and Vietnam's Viettel that could make or break their debut ACL campaign.

ASEAN's other sides could make a difference in group stages

The opening exchanges also proved that Southeast Asian sides in the competition may not be mere pushovers in the group stage, and could play a significant role in deciding which teams could advance to the Round of 16.

There have been a handful of good performances by the newcomers from ASEAN. While JDT and Pathum United came away with wins, it was 2020 V.League 1 champions Viettel who caught the eye most despite not collecting any points.

Playing against last year's winners Ulsan, Viettel were unfazed by the challenge and fought shoulder-to-shoulder against the Tigers in the Group F clash. It was only a late strike from Lukas Hinterseer in the final seconds that ended their resistance in their first outing in the tournament.

Elsewhere in Group I, Philippines Football League champions United City were left to rue plenty of missed chances as they were held to a 1-1 draw by a weakened Beijing Guoan in their opener at the Bunyodkor Stadium in Tashkent.

Will it be the third time lucky for Johor Darul Ta'zim?

Despite pulling off a few commendable displays here and there, Johor's journey in the group stages of the Champions League has been one of gloom. Their debut campaign in 2019 saw them upset former champions Kashima Antlers but finish bottom of the pack nonetheless.

The second season was even more catastrophic, but not due to any fault of their own. Despite a decent start stunning Suwon Samsung Bluewings, JDT were unable to resume their campaign in Doha due to the travel restrictions set by the Malaysian government due to the COVID-19 pandemic.

The 2021 campaign also began with disappointment as they were denied a point against Nagoya Grampus in the opener. However, they have since bounced back with a 1-0 win against Thai side Ratchaburi Mitr Phol on the second match day to occupy second place in the group.

It won't be an easy task making it out of the group as winners or one of the three best second-placed teams, but Benjamin Mora's wards have given themselves a fighting chance in the days to come as they try to reach their first-ever knockout stage appearance.

Second-string Chinese sides leave the race wide open

Chinese Super League sides have had a permanent presence in the knockout stages of the Champions League. But be very surprised if either of the two Chinese sides in the tournament make it to the Round of 16 this time around.

China had faced setbacks even before the start of 2021 ACL after local champions Jiangsu ceased to exist due to financial troubles while, Chinese FA Cup winners Shandong Taishan failed to meet AFC's licensing criteria to play continental football. Meanwhile, Shanghai Port FC were eliminated in the qualifying play-offs by Kaya.

It is left to Guangzhou FC and Beijing to fly the flag for China but both have sent junior sides to the competition due to pandemic restrictions, while their first teams stay on in China to play in the domestic league.

This means that we could see some new faces in the knockout stages in 2021. Will it be teams from Japan and South Korea, who usually produce the frontrunners of the competition? Or could it be the ASEAN sides who will capitalise on the situation?