Thai Premier League Wrap: Chainat hold Muang Thong
The league leaders held a two-point advantage at the summit heading into Wednesday's fixtures, but are now reliant on goals scored for their top position.
Breathing down their necks are BEC Tero Sasana, who were left requiring just one more goal to go top as they triumphed 2-0 over basement club Samut Songkhram.
Chanathip Songkrasin and Sho Shimoji scored either side of the break to give the hosts a healthy lead, before both sides had a man sent off.
The result sent them level on both points and goal difference with Muang Thong United, who now have just two wins from their last six matches.
Defending champions Buriram United held on to third spot, but were made to work for their 3-2 victory at Songkhla United.
After Carmelo Gonzalez and Nattawut Sombatyotha appeared to put the visitors in control of the clash, Faysal Shayesteh and Ekkachai Nuikhao pulled the home side level before the break.
However, Javier Patino popped up 14 minutes from time to seal the three points.
Chonburi also won 3-2, as they pipped Police United despite initially letting a two-goal lead slip.
There were also wins for Singhtarua and Chiangrai United, who beat PTT Rayong and Bangkok Glass 2-1 and 2-0 respectively.
Samut Songkhram remain rooted to the bottom of the league after their defeat to BEC Tero Sasana, but fellow strugglers Sisaket and Bangkok United pulled off important victories.
Sisaket were 1-0 winners at Osotspa Saraburi and climb above Chainat Hornbill and out of the relegation zone, while Bangkok United marched past Army United 3-0 to edge closer to safety.
Elsewhere, TOT triumphed 2-1 over Air Force Central, who remain mired in the relegation battle, while Ratchaburi beat Suphanburi 3-0.