Masahiro Wada's side secured an impressive victory over Buriram last time out as the defending champions saw their 19-game unbeaten league run brought to an end.
But While Chonburi climbed within a point of the summit as a result, they failed to build on the win, as Singhtarua upset the odds to claim their first point in six games.
The hosts took the lead through Thiago Cunha after an hour, but Singhtarua levelled through Ekaphan Inthasen just three minutes later and held out to frustrate the hosts, who now trail Buriram by three points.
Buriram had comfortably seen off strugglers Air Force Central 24 hours earlier as goals from Javier Patino and Adisak Kraisorn either side of the break condemned Air Force to a 15th league defeat of the season.
With eight games remaining, Wada's men retain only a slender one-point cushion in second place after Muang Thong United and BEC Tero Sasana both picked up points on Saturday.
Muang Thong were held to a goalless draw by Suphanburi, which allowed Tero Sasana to close the gap between third and fourth to just two points.
First-half goals from Sho Shimoji and Georgie Welcome were enough to see off Chainat Hornbill 2-1.
Police United's 1-1 draw with fellow strugglers Songkhla United failed to move them out of the bottom five while TOT will also be looking over their shoulder after Fabio Lopes' goal condemned them to a 1-0 defeat against Ratchaburi.
Chiangrai United were denied three points by Ekkapan Jandakorn's late leveller against Sisaket, while the Bangkok derby ended all square at 1-1.
Milos Bogunovic opened the scoring for Bangkok United in the capital after 80 minutes only for Phuritad Jarikanon to level for city rivals Bangkok Glass in the latter stages.
There were goals aplenty at the New Rayong and Samut Songkhram Stadiums.
PTT Rayong edged Osotspa 2-1 as their mini-revival continued with Samut Songkhram staging a comeback to take a point off Army United in a 2-2 thriller.
