Kumuls winger Garry Lo was the difference, running for a game-high 200 metres, breaking 15 tackles and scoring a try.
His performance was a highlight in an error-riddled contest, with both sides pushing the pass and struggling to execute when it mattered most.
Leading 8-6 at half-time, PNG could not put the game away and it left the door open for an unlikely Irish victory.
Second-row forward Louie McCarthy-Scarsbrook came within inches of becoming an Irish hero, knocking on over the goal line with 10 minutes to go.