Thai League 1 champions BG Pathum United beat FA Cup winners Chiang Rai United 1-0 in the Thailand Champions Cup match in Chiang Mai on Wednesday night.
Substitute Ryo Mutsumura scored the winner after 87 minutes to finish off the Beetles who were reduced to 10 men in the curtain-raising match for the new season.
Chiang Rai defender Brinner was sent off for tripping his Brazilian compatriot Diogo Luis Santo outside the area in the 18th minute.
It was one-way traffic but the Rabbits failed to find the back of the net until Mutsumura's strike.
The 2021/22 season will begin on Friday with promoted Nong Bua Pitchaya facing Nakhon Ratchasima in Thai League 1.
Chiangmai United and Khon Kaen United are the other two newcomers.
The start of the new season has been postponed twice due to a surge in Covid-19 cases.
The Football Association of Thailand (FAT) announced this week that the upcoming season will be the beginning of a 'new era.'
BG Pathum are favourites to retain the Thai League 1 title after winning their first ever top flight crown last season ahead of Buriram and Port.
After guiding the Rabbits to the title, coach Dusit Chalermsan left for Thai League 2 side Rajpracha before joining Port.
Pathum are now coached by Australian coach Aurelio Vidmar who helped them reach the knockout stages of the AFC Champions League recently.
Buriram and Port are among contenders to lift the trophy in May.
Matches in the top flight will be shown live on Channel 5 and PPTV, and via AIS Play online and smartphone platforms.
