Buriram have made a poor start to their title defence, having collected just four points from as many matches this season.
They sit in the bottom half of the table after an excellent performance from Bangkok Glass, who moved up second with their win.
Thailand international Teeratep Winothai was the hero for the victors, scoring twice.
Bangkok Glass now sit just one point behind leaders Muang Thong United, who cruised to a 4-0 win over Songkhla United on Saturday. Four different players scored for Muang Thong, who remain undefeated in the campaign.
Leandro's stunning start to the season continued as he helped Singhtarua claim a 2-2 draw at Bangkok United on Sunday.
The Brazilian midfielder has been the competition's star man in the first four rounds of competition and another excellent performance saw newly promoted Singhtarua come from behind to win a point.
Singhtarua sit fifth in the table after Leandro scored in both halves of the draw, with the 31-year-old's brace giving him six goals for the season, enough to top the league's scoring charts.
BEC Tero Sasana sit third after a 1-1 draw with Chonburi on Sunday while Ratchaburi moved to fourth after toppling Air Force Central 2-0 one day earlier.
Rock-bottom Samut Songkhram lost 4-2 at Chiangrai United, who won for the first time this season.
Other results saw Army United win 3-1 at Police United while TOT beat Sisaket by the same scoreline.
Elsewhere, Suphanburi edged PTT Rayong 1-0 and Chainat and Osotspa played out a 1-1 draw.
