Heavy downpour forced competition to start an hour behind schedule but it did not slow down the Beetles, the 2017 runners-up who lost to Buriram 2-0 in the final.
Chiangrai’s winning goal was produced by Brazilian William Henrique whose attempt was denied by Narit Taweekul but the ball bounced into the net in the 65th minute.
Chiangrai won the winner’s cheque of Bt5 million while Bangkok Glass had to settle with Bt1 million prize money as runner-up. The four previous Cup winners were Thai Port, Buriram, BEC Tero and Muangthong.