Bangkok United went down 3-2 to two-time AFC Champions League winners Jeonbuk Motors of South Korea in their last Group F game Wednesday night.
The Angels, who have had a sterling run in the tournament, finished as group winners with their South Korean opponents taking second spot after the home victory.
Jeonbuk also qualified for the knockout stage, advancing as one of the three best runners-up from the East zone.
Bangkok United went ahead early in the match when Nitipong Selanon crossed the ball for Wanchai Jarunongkran to tap it home.
Jeonbuk equalised in the 41st minute as Peerapat Notechaiya and Nitipong Selanon let a cross from Lee Dong-Jun make its way to Moon Seon-Min.
Jeonbuk got their second goal after 76 minutes from a counter-attack by Lee Dong-Jun.
Two minutes later, the home team consolidated their advantage when Lee struck again to make it 3-1 in favour of Jeonbuk.
Bangkok United reduced the deficit to one goal in the 85th minute when Peerapat curled in a corner for Rungrath Phumichantuk to score.