Reigning champions Buriram had no problem in disposing of fifth-placed Chiangrai, with five different goalscorers helping the new leaders to extend their unbeaten top-flight run to 16 matches.
Muang Thong themselves were on a fine run of form heading into the midweek games, having not lost in 13 league outings, but BEC Tero Sasana provided an upset at the SCG Stadium as they won 1-0 courtesy of Jaturong Pimkoon's late winner.
Three sides now sit level on 50 points at the top of the table, with Chonburi's 1-0 victory over second-bottom PTT Rayong - their seventh win in a row in all competitions - moving them level with Buriram, who lead the way on goal difference ahead of Muang Thong.
At the other end of the table, basement club Samut Songkhram started life without coach Paiboon Lertwimonrat with a 2-1 defeat at Suphanburi.
Lertwimonrat had resigned after the weekend defeat to Singhtarua but a change in the dugout did little to lift the struggling visitors.
Elswhere, Air Force Central lost a five-goal thriller 3-2 at home to Bangkok Glass while Songkhla United, who sit 17th, lost by the same scoreline at Sisaket - for whom Brent McGrath scored twice.
Police United shared six goals equally with Osotspa at the M-150 Saraburi Stadium, while TOT slipped nearer to the relegation zone as they fell to their fifth straight Premier League defeat, losing 2-0 at mid-table Bangkok United.
Chainat Hornbill's chances of survival were boosted further by their superb 2-1 away win at sixth-placed Singhtarua and Army United moved up to eighth with a 2-1 success at home to Ratchaburi.
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