Coach Rangsan Viwatchaichok began his stint at Port with a 1-1 draw at Chiang Rai United in Thai League 1 on Sunday night.
Port got off to a lively start but it was the hosts who went in front in the 24th minute when Bill Rosimar beat goalkeeper Somporn Yos with a long-range shot from just inside Port's half.
The visitors dominated for long periods in the second half and their efforts were rewarded after 78 minutes when Iraq's Frans Putros headed home a corner to make it 1-1.
Bill almost beat Somporn with another long-range drive in the 87th minute but the goalkeeper was quick to deny his attempt this time.
In Sunday's other game, newcomers Uthai Thani lost 1-0 to Police Tero who are under interim coach Worawoot Srimaka.
The winning goal came in the 16th minute when Sorawit Panthong's curling free-kick found its way into the net as Uthai goalkeeper Boonyakiat Wongsajam failed to get to the ball.
The goal proved enough to seal three points for the Fire Dragons.
Pathum face Ulsan
High-flying T1 club BG Pathum United will try to get their first point of the 2023-2024 AFC Champions League campaign when they host South Korea's Ulsan on Tuesday.
The Thais, who are now second in the domestic league, have lost all their first four games in Group I.
Ulsan have six points and are ahead of Malaysia's Johor on goal difference.
Runaway Group I pacesetters Kawasaki Frontale (12 points) are at home to Johor on Tuesday.
"This will be our last home match so we will do our best and try to get at least a point," BG coach Surachai Jaturapattarapong told a press conference on Monday.
"We have to get a good result to boost our confidence for the domestic competition."
Ulsan coach Hong Myung-Bo said: "The weather in Thailand is completely different to South Korea. We still have two matches so we believe that we do have a chance to qualify."