Former Thai League 1 winners Chiang Rai United were handed a 1-0 defeat by Kitchee SC of Hong Kong in their first AFC Champions League Group J game in Buri Ram on Saturday night.
All the Hong Kong club needed to seal the win was a right-footed shot by Ruslan Mingazov from the centre of the box to the bottom right corner following a low cross from Law Tsz-Chun in the 17th minute.
The Beetles had a few chances after the break but still ended up on the losing side.
Earlier on Friday night, BG Pathum United coach Makoto Teguramori praised his men after the Rabbits pulled off a rallying 1-1 draw with Australian champions Melbourne City in their Group G opener.
The A-League champions looked set for a winning debut when Andrew Nabbout fired them ahead in the 22nd minute, but Teerasil Dangda's equaliser 13 minutes later meant the spoils were shared.
Teguramori said he was relieved that the Thai side were able show their true potential after adjusting to Melbourne City's intensity.
"[Our slow start] was because the players were a bit frightened of the game," said the former Vegalta Sendai boss. "It was their first game and they were nervous, but as the game went on the players got more comfortable, and we were able to stick to our plan.
"During the half-time break we had a talk about the tempo and how we can switch up the play in the second half, and the players really responded to that well.
"In the second half the players got more used to the tempo of the game, and that really took the weight off our backs and helped us to play in our way."
Pathum United will face group leaders Jeonnam Dragons in their next clash, while Melbourne City will be chasing a maiden win against United City FC of the Philippines.
In Thai League 1 games last night, Nakhon Ratchasima moved three points clear of the drop zone following a 1-0 home win over Ratchaburi while Muang Thong United rallied to a 1-1 draw at relegated Chiangmai United.