A 59th-minute goal from Charyl Chappuis saw Buriram edge the five-goal thriller on Sunday, having initially trailed to Sumanya Purisai's opener after nine minutes.
Buriram equalised on the 30-minute mark through Suchao Nuchnum and then went ahead through Barba Ibanez Osmar's penatly three minutes before half-time.
Hosts Chainat, though, hit back courtesy of Seon Power, but Buriram held their nerve to secure the win following Chappuis’ goal 31 minutes from time.
Victory ensured Buriram took full advantage of second-place Muang Thong United drawing 1-1 on Saturday against Chonburi, who are third. Adul Lahsoh cancelled out a Mario Djurovski strike as Muang Thong drew for the second weekend running.
To compound matters further, Datsakorn Thonglao was sent off for the defending champions for lashing out at Kazuto Kushida.
Suphanburi slipped to back-to-back league defeats with a 5-2 loss at home to Police United and Army United were held to a goalless draw with Ratchaburi.
The thrashing at the hands of Police United leaves Suphanburi four league games without a win as five different scorers were on target for the Pathum Thani side, with Surachart Sareepim completing the rout in the 90th minute.
Bangkok Glass and Pattaya United won 2-0 and 2-1 against Chiangrai United and BEC Tero Sasana respectively.
Bangkok Glass had goals from Goran Subara and Lazarus Kaimbi to thank for their victory, while Pattaya left it late as Ajoku Obinna netted a winner in the 90th minute to edge his side six points clear of the drop zone and record a third win in a row.
Fellow strugglers Samut Songkhram drew 0-0 with TOT to leave them in 16th place. The clash between Bangkok United and Osotspa also ended goalless as Chalermwoot Sa-Ngapol’s men continued a poor run of form that has seen them pick up just one win in six.
