New Zealand A 252 all out in 49.12 overs (Anton Devcich 62, Colin Munro 50, Martin Guptill 41) lost to Ireland 253-6 in 44.0 overs (Nathan McCullum 2-26) by four wickets.
New Zealand A suffered the first defeat of their tour to a determined Ireland side, who were lead by Andy Balbirnie's maiden List A hundred.
Martin Guptill (41) and Anton Devcich (62) got NZ A off to a strong start to the innings - the pair made 102 together at a good clip until Guptill, then Devcich fell victim to Kevin O'Brien in the 19th, then 23rd overs.
O'Brien then made a double strike in the 25th over to remove Dean Brownlie for two and Luke Ronchi for a duck to halt the innings' momentum.
Hamish Rutherford (28) and Colin Munro (50) put on 42 together to turn things around, before Nathan McCullum made 34 to give the total some respectability, but when Matt Henry was last man to go from the first ball of the 50th over, 252 felt light.
Ireland's reply was set up by a Niall O'Brien and Andy Balbirnie's 133 run stand for the second wicket. Adam Milne removed the former for 68 from 67 balls caught by Martin Guptill, but Balbirnie carried on, eventually being caught by Brownlie from McCullum's bowling for 129 from 96 deliveries, when the score was on 231 and the finishing line was in sight.
Ireland reaching their target with six overs remaining - McCullum was the pick of the NZ A bowlers, recording 2-26 from his nine overs.
The two teams meet again at 7pm Monday night NZ time.