It will have been a case of more frustration in the home changing room as well after William Porterfield's side collapsed from 212-5 to 238 all out despite O'Brien's heroics.
The North West Warriors 'keeper/batsman was in sublime form as he built his innings patiently after the early loss of both Porterfield and Paul Stirling. O'Brien and Andy Balbirnie (36) added 86 for the 3rd wicket and although younger brother Kevin came and went soon after, Gary Wilson (30) helped his partner take Ireland to within 78 runs of a stunning victory.
It wasn't to be however as Mitchell Santner turned the game on its head in his second spell to finish with figures of 5-50 as Ireland's lower order succumbed to spin again- O'Brien himself one of that quintet after making a career-best ODI score of 109 (9 fours, 5 sixes). Scott Kuggeleijn also impressed with 3-31 as Ireland's lower order gave way as the required run-rate increased.
The Black Caps had made a commanding 289-7 in their 50 overs with all the top order among the runs. Luke Ronchi (37) and Tom Latham (15) put on 53 for the first wicket before both fell in quick succession to Barry McCarthy.
Simi Singh is stumped
George Worker and Ross Taylor gave their side a foot-hold in the contest after that with an 84-run partnership- both men helping themselves to half centuries in the process- before Neil Broom upped the ante with a 63-ball 79 (9 fours and a six).
Jimmy Neesham's 30 pushed the Kiwis to within touching distance of 300 but the hosts bowlers did really well to keep them below. McCarthy (2-59) was again the pick, especially early on as he gave his side a much-needed lift, however Tim Murtagh (2-62), and Kevin O'Brien (1-46) provided good support.
Porterfield's men have a few day's off now before their second game against Bangladesh at the same venue on Friday (10.45), but before that New Zealand take on Bangladesh at Clontarf on Wednesday.