You are not permitted to download, save or email this image. Visit image gallery to purchase the image.
Ireland looked to be coasting with five overs to go in Dublin, in their hunt to overtake the Black Caps' formidable 360 runs.
Centuries from Paul Stirling (120) and Harry Tector (108) set the platform for Ireland, who at one stage were at 271 for three, but quick wickets and tight bowling saw the Irish chase start to collapse.
The hosts still had a shot and needed 10 runs off the final over, and then three runs from the final ball.
But they could only scramble through for a bye on the last ball, giving the Kiwis the victory by the slimmest of margins and the 3-0 series sweep.
It was the second heartbreaking loss for Ireland, who could have won the first ODI if not for the heroics of Black Caps all-rounder Michael Bracewell.
Earlier, New Zealand reached 360 for six with opener Martin Guptill, who took out the player of the match award, top scoring with 115.
Black Caps captain Tom Latham was delighted with the way his side responded to Ireland's challenge.
"We saw it as the best wicket we've seen [all series] … We thought we would get a good score on the board and we'll be able to defend it.
"Full credit to the way Ireland came out and played. I thought Harry [Tector] and Paul Stirling put on a wonderful partnership. They certainly put us under pressure but really happy with the way our guys responded, especially in the last 10 overs being put under all that pressure by a quality side. It's nice that we came out on top."
The Black Caps bowlers managed to get the job done in the end, with Mitch Santner's three for 71 crucial in the second spell. Matt Henry was also massive, bagging four for 68.
Latham praised Santner and the rest of the bowling team.
"[Santner] was great. Obviously he's a world-class bowler who has great control. And certainly in those phases of the game when guys are coming at him, he's a pretty crafty customer.
"I thought all the guys that came in that back end were looking to take wickets and they were pretty clear on the plans, in terms of what they wanted to do. I thought it was a great effort towards the back end."
The Black Caps will next face Ireland in a three-match T20 series, starting on Tuesday morning.
Scores: New Zealand 360 for 6; Ireland 359 for 9.