An injury time goal ensured South Korea's Ulsan Hyundai kicked off the defence of their Asian Champions League title with a narrow 1-0 win over Viettel from Vietnam in Bangkok on Saturday.
Hong Myung-bo's side laboured against the group stage debutants until Lukas Hinterseer and Nguyen Thanh Binh's six-yard box tussle saw the ball roll over the line to hand last year's winners the three points in the Group F meeting.
Ulsan join BG Pathum United as opening day winners in the group after the Thai side handed tournament newcomers Kaya-Iloilo from the Philippines a 4-1 thrashing, with Teerasil Dangda and Diogo both scoring twice.
Teerasil put his team in front from close range in the 23rd minute and Diogo rounded goalkeeper Louie Casas to score the second 10 minutes before the break.
Simone Rota's sending off four minutes into the second half added to Kaya's woes and by the 51st minute Diogo had added his second with a low free kick before setting up Teerasil to score with a header eight minutes later.
That left Marwin Angeles to score a consolation for Kaya nine minutes from time.
In Group I in Tashkent, Japanese champions Kawasaki Frontale twice came back from going behind to complete a 3-2 victory over Daegu FC from South Korea to open their campaign with a win.
Leandro Damiao scored twice - including a spectacular overhead kick - to cancel out efforts from Hwang Soon-min and Cesinho before Joao Schmidt netted the winner for Toru Oniki's side 10 minutes into the second half.
Stephan Schrock gave United City FC of the Philippines the lead in their meeting with Beijing Guoan as the former German youth international curled home his effort from the edge of the area.
But Liang Shaowen's free kick earned a 1-1 draw for Beijing, who have sent a young squad to the competition due to strict quarantine restrictions in China limiting their ability to send a full strength line-up.
Group stage matches in the Asian Champions League for clubs from the east of Asia are currently being played in Thailand and Uzbekistan in biosecure hubs.
The top team in each of the five groups will advance to the knockout rounds alongside the three best runners-up.
Teams in the west have already completed the group phase and the Round of 16 is due to be played in September, with the final scheduled for late November.