Third represented their best result at the tournament since 2017.
Ireland took the early lead. They soaked up some early pressure then pounced with their first appearance in the 22m.
Halfback Oliver Coffey finished off following some hard work by the pack.
Irish fullback Ben O’Connor helped put Ireland further ahead when he busted through, drew the defence and offloaded to first five Jack Murphy, who dived over in the corner.
Otago halfback Dylan Pledger sparked the response. He set up hooker Vernon Bason, who charged over to cut the gap to 12-7 at halftime.
New Zealand winger Frank Vaenuku got a yellow card early in the second half. But New Zealand had all the momentum.
Bason cut through on a 30m burst to the corner for his second try.
Then centre Aki Tuivailala jigged his way through traffic and got the ball to fellow midfielder Xavier Taele, who ran 10m and slid in the other 5m to score.
Vaenuku made amends for his yellow card with two tries.
He got on the end of a cross-field kick to score and scooped up a deflection to dive over for a second.
Ireland finished strongly with a couple of tries.
Midfielder Hugh Gavin impressed. He made 17 tackles and found a lot of space late in the game.
Loosehead prop Alex Mullan also had a busy shift for Ireland.
Taele carried strongly for New Zealand, and tighthead prop Joshua Smith was tireless on defence.
England beat France 21-13 in the final. It was their first title since 2016.
France were chasing a fourth consecutive U20 crown.
Under-20 playoff
The scores
New Zealand 38
Vernon Bason 2, Frank Vaenuku 2, Xavier Taele, Jeremiah Avei-Collins tries; Rico Simpson 4 con.
Ireland 24
Oliver Coffey, Jack Murphy, Ethan Graham, Sean Naughton tries; Murphy 2 con
Halftime: Ireland 12-7.
