Bottom club Chiangmai United stunned Port 2-1 at PAT Stadium in Thai League 1 on Sunday night.
Thawin Budsombut and Ekanit Panya were on target for the White Elephants and Kewin Deeromram scored for the home side.
Chiangmai went in front after just 38 seconds with Thawin scoring from close range.
Four minutes after the break, Ekanit made it 2-0 before Kewin cut the deficit to 2-1 in the 70th minute.
Chiangmai United received 500,000 baht from team manager Srisopha Kotkhamlue as a reward for the win.
Despite the victory, Chiangmai still have a mountain to climb to stay up in the top flight as they are nine points from safety.
At Chonburi Stadium, Police Tero upset Chonburi 2-1 thanks to Arthit Budjinda's last-gasp goal.
Yodsak Chaowana gave Police Tero the lead after 71 minutes and Gigi Kanyuk equalised for the hosts four minutes later.