PNG raced away to a 10-0 after only 15 minutes of play in the first half through a double from hooker Nathan Tente.
Behind on the scoreboard early in the game, NSW found their rhythm quickly and fought their way back.
The visitors found the try line 10 minutes out from half time when Jake Collins scored out on the wing.
A successful conversion further narrowed the score down to 10-6 going into the break.
Poor ball handling from PNG did no good for them as they gave away too much possession to NSW.