JJ Garth's Man-of-the-Match four wicket haul coupled with an invaluable 43 from Neil Rock saw Ireland beat Papua New Guinea by three wickets in a low scoring contest in Rangiora.
Josh Little (2-18) struck twice early on, and with Mark Donegan hitting the stumps direct with a brilliant piece of fielding, PNG were in trouble at 22 for 3.
Igo Morea (45) and Heagi Toua (39) shared a fourth wicket stand of 78 to put their side in a strong position, before Ireland struck back with a vengeance.
Garth (4-18) and skipper Harry Tector (3-32) tied PNG up in knots as they lost seven wickets for 21 to be dismissed for a modest 121.
Any thoughts the Boys In Green had that the run chase would be a formality were quickly dispelled as they found the track equally as tricky as PNG, who came out fighting.
Mark Donegan, Andrew Vincent, Harry Tector and Morgan Topping all fell cheaply and at 38 for 4, the match was evenly poised.
Rock though was solid as he expertly steered his team towards their target, top scoring with 43 as he shared partnerships of 33 with Jamie Grassi (24) and 45 with Graham Kennedy (17*).
The Rush left-hander fell with just six runs needed, and Josh Little's dismissal one run later saw a few nerves in the camp before the three wicket win was eventually sealed.
"We started the game really well with Josh taking a wicket in his first over, and had them three down very quickly," said Rock afterwards.
"After that we went searching a bit with the ball and allowed them to build a decent partnership. We came back strongly and I thought JJ Garth bowled really well, using his variations and spun the ball both ways.
"There was a great improvement today in our fielding after letting ourselves down in the last game against the West Indies.
"PNG bowled very well, stump to stump and disciplined on what was a difficult, low, slow pitch.
"I knew that all it would take was one or two partnerships and thankfully that was what we got with myself, Jamie Grassi and Graham Kennedy sharing decent stands to seal a tough win."
Ireland now play Namibia on Saturday in the 13th-14th play-off match.
U19 World Cup Play-Off, At Rangiora.
Papua New Guinea 121 all out (37.1 overs; Igo Mahuru 45, Heagi Toua 39; JJ Garth 4-18, Harry Tector 3-32, Josh Little 2-18)
Ireland 122/7 (41.5 overs; Neil Rock 43, Jamie Grassi 24; James Tau 4-45, Semo Kamea 2-22)
Ireland beat Papua New Guinea by three wickets