Port defeated PT Prachuap 3-1 on Sunday night to reclaim a share of the top spot in Thai League 1.
At PAT Stadium, hosts Port went in front after 40 minutes when defender Kevin Deeromram beat Prachuap goalkeeper Pisan Doakmaikaew.
Port were the better side in the second half with Barros Tardeli and Bordin Phala squandering several chances.
The hosts had to wait until the 88th minute to get the second goal from Chanukan Karin's header.
Samuel Rosa cut the deficit to 2-1 in injury time only for Teerasak Poeiphimai to make it 3-1 in the dying moments.
After four games, Bangkok United, Buriram United, Port and Chiang Rai United all have 10 points.
Pathum face Ulsan
Thai League 1 side BG Pathum United begin their AFC Champions League campaign at Ulsan Hyundai in South Korea today.
In today's other Group I match, Malaysia's Johor Darul Ta'zim host Japan's Kawasaki Frontale.
Reigning Korean champions Ulsan will be hoping for better luck as they look to redeem themselves after failing to advance from the group stage in 2022.
Pathum, however, are not worried about facing Ulsan, with the Thai side aiming to better last season's quarter-final finish.
"Fatigue from our latest match and from travelling may play a part but all of our boys are determined and are fully fired up for tomorrow's match," Pathum technical chairman Surachai Jaturapattarapong told a press conference yesterday.
BG captain Sarach Yooyen said: "Everyone is aware of the fact that we are placed in a difficult group. However, our club and players share the same goal -- that is to qualify for the next round."