Title chasers Port suffered a stunning 6-3 defeat at Samut Prakan City in the Thai League 1 action on Sunday night.
Port had hoped for an away victory as they attempted to close the gap on leaders BG Pathum United who defeated Prachuap FC 2-0 on Saturday to move 10 points clear.
Second-placed Port remained on 34 points after 15 games, 10 behind BG Pathum who played 16 games. Samut Prakan stayed sixth on 25 points after 16 games.
Yesterday's defeat also ended Port's winning run. Since coach Sarawut Treephan took over the club's top job in September, the Lions have won 10 consecutive games in all competitions.
Teeraphol Yor-Yoey, Jaroensak Vongkorn, Peerapol Chamratsamee, Suphanan Bureerat, Tardeli Reis and Aris Zarifovic were on target for the home side while Sergio Suarez, Adisak Kraisorn and Nelson Bonilla scored for Port.
Bonilla scored the third goal for Port in the 71st minute but two goals from Reis and Aris in the last 10 minutes of the game ended the visitors' hope of a comeback.
Port fell two goals behind after just seven minutes with goals from Teeraphol and Jaroensak.
Suarez revived the visitors' hope with a 25th-minute penalty but Samut Prakan captain Peerapol Chamratsamee converted theirs in the 39th to restore the two-goal advantage.
Port's Adisak made it 3-2 just before half-time but Suphanan again extended the lead in the 56th minute.
Earlier, a goal by Trat's Pornpreecha Jarunai after just eight minutes was enough for the visitors to beat hosts Police Tero.
The skipper fired a fierce left-foot shot from the edge of the box past goalkeeper Prasit Padungchok. The victory lifted Trat off the bottom place.
Police Tero played the last 10 minutes of the game with 10 men when Chompoo Sangpo was sent off after a second bookable offence in the 81st minute.
In the day's other game, hosts Nakhon Ratchasima defeated Rayong FC 2-0.
Israel midfielder Gidi Kanuk broke the deadlock in first-half added time and Ivory Coast forward Amadou Ouattara completed the scoreline in dying minutes.