Buriram are awaiting the outcome of an investigation into allegations that match-fixers tried to rig the result of their FA Cup final victory against Army United in November.
Thai Football Association head and FIFA executive committee member Worawi Makudi said last week that the Japanese official in charge of the final, which Buriram won 2-1, had reported to the Asian Football Confederation that he had been offered money to help rig the result.
The Thai team, however, put the controversy behind them in the Group E opener at a snowy Sendai Stadium and equalised through captain Osmar Barba Ibanez in the 76th minute to take home a point. Ryang Yong-Gi had converted a penalty to put the hosts ahead in the 53rd minute.
Buriram beat J League team Kashiwa Reysol 3-2 in a memorable AFC Champions League debut last year but lost the return game in Japan by a solitary goal.
The Thai club, who edged out Australia's Brisbane Roar on penalties in the play-offs to make their second successive group stage, host FC Seoul in their next group fixture on March 12.