Port conceded a last-minute penalty to settle for a 2-2 draw in a Thai League 1 battle at Ratchaburi on Sunday night.
Ratchaburi were the first to score as Pongsakorn Sangkasopha put them ahead in the 15th minute.
Port equalised in the 34th minute when Asnawi Mangkualam set up Worachit Kanitsribumphen.
The visitors claimed the upper hand two minutes before the break when Brazilian Felipe Amorim won a penalty and converted it.
However, Port were dealt a big blow six minutes into the final added time when Chalermsak Aukkee was red-carded and Tyronne del Pino converted the penalty to earn a point for Ratchaburi.
In the other match on Sunday night, hosts Nakhon Pathom United suffered a 3-1 defeat at the hands of star-studded BG Pathum United.
Khon Kaen United moved to seventh place in the league standings following a 5-1 hammering of Sukhothai on Sunday night.
Buriram United have already assured of the Thai League crown after opening an unassailable gap at the top of the league table.