Opener Riley Hekure was the star with his knock of 115 off 64 balls.
Hekure smashed 10 fours and 6 sixes for PNG to set the target at 176.
Tonga’s openers in Aloisio Pau’u (13) and Nikolasi Moala (16) got Tonga off to reasonably good start.
The dismissals of the pair brought on to the crease Maamaloa Kuluka who top scored with 41.
But Kuluka eventually ran out of partners to help chase down the target as wickets fell in close succession.
Tonga’s innings came to an end at 5/108 after 20 overs.
Joel Tom for PNG took 2/16 off his three overs.
PNG A will play Vanuatu for gold at 2pm while Tonga plays New Caledonia for bronze.