Ireland had won two of their three contests, most recently last September, but a much-changed New Zealand — there were only nine survivors from the 29-27 loss last year — proved far too strong, too quick and too slick on Sunday (Monday AEST) after two stuttering wins over Spain and Japan.
This felt like a statement of intent as teenage sensation Braxton Sorensen-McGee finished three of New Zealand's six tries — her second successive World Cup hat-trick.
Renee Holmes made five conversions from the sideline and had a late end-to-end try ruled out by a slight knock-on.
Both teams were already through to the quarter-finals but New Zealand, by winning the pool, will play South Africa, who were hammered 57-10 by France in the pool D clash in Northampton.
Group runners-up Ireland will next play France, hoping co-captain Edel McMahon and fullback Stacey Flood are available after leaving injured.
Ireland were up for the Pool C decider, starting a staredown after the Black Ferns' haka. That ramped up the tension in the 31,000-strong crowd.
They also started well but couldn't get across the line, a running theme. New Zealand were ruthless at the other end, focusing effective pressure on Irish playmaker Dannah O'Brien. The forwards constantly broke the line and the backs kept hitting the Irish behind the gain line.
The 18-year-old Sorensen-McGee gave the last pass for Stacey Waaka to score the opening try, then prop Chryss Viliko powered over from lineout ball. Sorensen-McGee's first try, set up by Portia Woodman-Wickliffe and Waaka, put them 19-0 up at halftime.
Ireland had try chances in the second half, but the ball bounced out before Amee-Leigh Costigan could touch it and hooker Cliodhna Moloney-MacDonald was held up over the line.
Meanwhile, Sorensen-McGee was set up for two more tries by her fellow backs, and New Zealand capped a statement win after the fulltime hooter by running out from their 22.
Ayesha Leti-I'iga, Sorensen-McGee and Jorja Miller combined to send in Maia Joseph, and Holmes' touchline conversion gave them their biggest win against Ireland.
Japan earned a first pool match win in 31 years after seeing off Spain 29-21 in York, coming from 14-5 down at half-time to grab the glory, while Italy beat Brazil 64-3 for their record-high World Cup win.
