BG Pathum United's bid to retain their Thai League 1 title was thrown off the track again after a goalless draw at struggling PT Prachuap on Sunday night.
The result ensured the Rabbits remained winless under new coach Dusit Chalermsan for the third league game in a row.
The champions are down to fifth place at the end of the first leg of matches in the top league.
Things would have been worse for Pathum United had not the hosts wasted a couple of chances in the first half.
The Rabbits improved in the second half but the only real scoring opportunity they had was headed off target by Chatree Chimtalay.
Meanwhile, Yoo Byung-Soo netted on either side of the break as Chonburi took over third spot in the table following an impressive 3-0 home victory over Ratchaburi.
Worachit Kanitsribumphen was on target for Chonburi's third goal a few minutes after the hour mark.
Ratchaburi did bother Chonburi with repeated forays but the home team's defenders were able to keep them from scoring.
On Saturday night, Japanese coach Masatada Ishii's two-year reign at the helm of Samut Prakan City ended in a 1-0 away loss at the hands of Khon Kaen United.
Ishii announced last week that he would quit his job at the end of Samut Prakan's trip to promoted Khon Kaen when his contract with the struggling team came to an end.
Ibson Melo scored the winning goal for Khon Kaen in the 15th minute of the match.
Also, Police Tero picked up three points at home after a 1-0 win over Chiangmai United.