They also presented a disciplined defensive line, shutting down the Black Ferns so well that dangerous outside backs Honey Hireme and Huriana Manuel hardly saw any ball.
The latter did have a hand, though, in a try to fullback Selica Winiata, against the run of play from a turnover. But the 8-7 halftime lead was flattering to the Ferns.
They started the second spell with more energy and purpose but made myriad errors forced and unforced, in the face of the fired-up Irish, who posted a sweet try to left wing Alison Miller. She burned halfback Emma Jensen on the outside.
Winiata was then held up over the line but that missed opportunity was indicative of the Ferns' inability to finish, the backs aligned too deep and the pack under strain.
Assistant coach Grant Hansen was not surprised at all by Ireland's physicality, having watched them do the same against USA, but he rejected any hint of complacency in the Black Ferns' camp.
"We had the utmost respect for the Irish. They were Six Nations champs a couple of years ago. We saw that they were up for it from the first whistle, so credit to them. They played very well," he said.
Flanker Rawinia Everitt was prominent with some heavy defence and carries, while Hansen paid tribute to captain Fiao'o Fa'amausili and Amiria Rule for leading from the front, but he admitted it was a disappointing overall performance from the defending champions.
"This will test the resilience and character of the girls, because they don't lose a lot," he added.
The USA beat Kazakhstan 47-7 yesterday and was in fact the last team to lower the Black Ferns at a World Cup, 7-0 at the unofficial 1991 Rugby World Cup.
Interested spectators were Ireland men's coach Joe Schmidt and French coach Philip St Andre, while Racing-Metro's Irish No 10 Johnny Sexton was also on hand.
Ireland (Heather O'Brien, Alison Miller tries; Niamh Briggs 2 con, pen) New Zealand (Selica Winiata try; Kelly Brazier 3 pen) Halftime: 8-7 New Zealand
