Port aim to claim the FA Cup after defeating Bangkok United in Thai League 1 on Sunday night.
Worachit Kanitsribumphen opened the scoring for Port after 12 minutes and Elias Dolah made it 2-0 in the 62nd minute.
Former Port player Nitipong Selanon cut the deficit to 2-1 in the 79th minute but the Angels could not find an equaliser.
In Sunday's last game, bottom club Nongbua, who were reduced to 10 men, stunned third-ranked Chonburi 2-1.
Champions Buriram, who defeated Prachuap 1-0 earlier on Sunday, now have a 12-point lead over Bangkok United.
"It was an exciting game. We want to get every point in every game we play in," said Port coach Surapong Kongthep.
Port next host Chiang Rai United in the FA Cup quarter-finals tomorrow.
"We want the trophy and we must keep on winning matches," Surapong said.
It was Totchatawan Sripan's first league loss in eight matches after his return to Bangkok Untied.
Totchatawan paid the price for resting some key players as he had an eye on the FA Cup quarter-final against Nakhon Ratchasima tomorrow.
"We lost concentration and conceded an early goal," he said.
"I have to apologise to our fans. In the next game, we must beat Nakhon Ratchasima for our fans who are disappointed by the result of this game [against Port]."
At Nongbua, Alvin Fortes gave the hosts the lead against the Sharks after just seven minutes only for Faiq Bolkiah to equalise in the 18th minute.
Nongbua's Adisorn Promrak was sent off in the 65th minute but Fortes scored the winner in injury time.