Hosts Suphanburi rallied to hand 10-man Port a 2-1 defeat last night that could prove costly for the Khlong Toey-based visitors in their quest for the Thai League 1 title this season.
Port were off to a good start with prolific Nelson Bonilla giving them the edge in the fourth minute.
However, Port were dealt a big blow in the 15th minute when Jaturapat Satthum was sent off for committing a handball inside the box. Ratchanat Arunyapairoj converted the penalty to even the score 1-1.
Port were never able to regroup after Jaturapat's exit and Suphanburi took control.
The hosts' domination could be ascertained from the whopping number of 21 shots they had on their opponents' goal compared to Port's only eight.
Port, who were expected to make an emphatic bid for this season's top-flight title, are now reeling in eighth place while Suphanburi have moved up to fifth spot.
Hosts Police Tero missed their opportunity to part company with the bottom three after they allowed Samut Prakan to pull off a 1-1 tie on Sunday night.
Police scored first in the 40th minute through Isaac Honny but Suphanan Burirat levelled it for Samut Prakan six minutes into the second half.
Also last night, hosts Chiangmai United remained winless after four matches following a 1-1 draw with Nakhon Ratchasima.