Mark Jackson's side were beaten 3-2 on Tuesday night (Wednesday AEDT) by Kevin Muscat's Shanghai Port, leaving them pointless and one off the bottom of 12-team Group A.
First-half goals from Shanghai's Li Ang - a header after two minutes following a corner - and Wu Lei, from close range, left  the Mariners facing a huge second-half challenge in China, following earlier defeats against Shandong Taishan and Buriram United
Doka halved the deficit in the 61st minute, cutting in from the left and thundering a shot in off the far post, to give the Mariners hope of a draw.
But Shanghai, with ex-Brazil and Chelsea star Oscar pulling the strings throughout, restored their two-goal advantage through Matias Vargas's clever low shot from just outside the area in the 86th minute.
Mikael Doka Special on a Tuesday �— #ACLElite | #ACLTwo (@TheAFCCL) #ACLElite | #SHPvCCM pic.twitter.com/TfB148hsrzOctober 22, 2024
Academy product Nicholas Duarte came off the bench to score his first Mariners goal - a fine shot inside the near post - in stoppage time but it came too late to avert another loss.
South Korea's Gwangju FC continued their perfect start to the league phase as Jasir Asani scored twice in his side's 3-1 win over Malaysia's Johor Darul Ta'zim to notch up a third victory in a row.
Thailand's Buriram United are second in the early standings following their 1-0 win over Pohang Steelers while Yokohama F Marinos, last season's runners-up, drew 2-2 with hosts Shandong Taishan.
Japan's Vissel Kobe take on former champions Ulsan HD on Wednesday aiming to close the gap on the leaders while Shanghai Shenhua will play Kawasaki Frontale.
Meanwhile, in Group B, Aymeric Laporte scored late on to give Cristiano Ronaldo's Al-Nassr to a 1-0 win over Esteghlal of Iran in Dubai.
Goalkeeper Seyed Hossein Hosseini frustrated Stefano Pioli's team until the 81st minute, when he pushed Ronaldo's goal-bound header high into the air and Laporte rose to nod in the rebound.
The win puts the Riyadh-based club onto seven points, two points behind their table-topping compatriots Al-Hilal and Al-Ahli.
Al-Wasl are a point further back after the side from the United Arab Emirates came from behind to defeat Qatar's Al Gharafa 2-1 in Doha.
The first eight finishers in the 12-team league phase in both east and west Asia will advance to the knockout rounds of the revamped continental championship, which will be played in March next year.
The quarter-finals, semi-finals and final will be played in a centralised format in Saudi Arabia in April and May.
