By Gabriel TanFollow @@gabetan13
The Twin Qilins took the lead at the United Stadium three minutes before the half-hour mark when Piyaphon Buntao struck, before Teerasil Dangda doubled their tally in the 58th minute.
Chiangrai did manage to pull one back eight minutes later when Leonardo Ferreira scored, but three minutes from time, Thailand winger Jakkapan Pornsai added a third to seal the win for the visitors.
The result was enough to send Muangthong two points clear at the top of the table, although nearest challengers Buriram United now have a game in hand.
Third-placed Chonburi were unable to fully close the gap on Buriram, who were in AFC Champions League action on Wednesday, as they were held to a 0-0 draw at home to Suphanburi.
Bangkok Glass bounced back from defeat at the weekend by cruising to an impressive 3-0 win over Army United at the Thai Army Sports Stadium.
It took the visitors just four minutes to break the deadlock when they scored through Hironori Saruta, before Lazarus Kaimbi added a second a minute after the half-hour mark.
Suphasek Kaikaew then got in on the act in the 48th minute to wrap up the three points for the Glass Rabbits, although their evening was tarnished eight minutes from time when Leandro dos Santos was sent off for a second bookable offence.
Jhon Obregon scored the only goal of the game a minute after the restart to hand Ratchaburi a 1-0 home win over TOT, while Samut Songkhram beat Songkhla United 2-0 thanks to second-half goals from Adisorn Daeng-rueng and Mark Babo.
BEC Tero Sasana relinquished a halftime lead as they fell to a shock 4-2 defeat against Chainat at the 72-years Anniversary Stadium.
After falling behind just before the break courtesy of an own-goal from Trindad and Tobago international Seon Power, the visitors equalised in the 59th minute thanks to a strike from Mbengono Yannick, who grabbed a second two minutes later to put his side ahead.
Ratchapol Nawanno then made it 3-1 in the 63rd minute, and although Dennis Buschening reduced the deficit for the Fire Dragons in injury-time, Yannick completed his hat-trick moments later to cap off a fine evening for Chainat.
Finally, Bangkok United made it two wins in a row after defeating Pattaya United 2-1 at the Nongprue Stadium.
After Paul Ekollo had given the visitors a 20th-minute lead, Romain Gasmi struck 14 minutes from time to put them in a commanding position.
Obinna Ajoku did pull one back for the Dolphins tin the 87th minute, but it proved to be too little too late as the Angels held on for the win.
Wednesday's Thai Premier League Results
Samut Songkhram 2-0 Songkhla United
Ratchaburi 1-0 TOT
BEC Tero Sasana 2-4 Chainat
Chiangrai United 1-3 Muangthong United
Pattaya United 1-2 Bangkok United
Chonburi 0-0 Suphanburi
Army United 0-3 Bangkok Glass
Image courtesy of Muangthong United FC