Men's lightweight double scullers Peter Taylor and Storm Uru struck Olympic Games reality on Dorney Lake with the resurgence of the British defending Olympic champions Mark Hunter and Zac Purchase.
Britain beat New Zealand by 0.73s - about half a length - after holding the lead for the entire race.
Taylor and Uru were 1.1-1.5s down on their rivals over the first 1500m but cranked into a fine final 500m to bridge the gap. Both crews progress to Thursday night's (NZT) semifinals.
At the two other World Cups in which New Zealand competed this season they finished with silver and gold medals. Britain finished sixth in both regattas but have clearly benefited by tapering from a strong fitness base.
Uru said the race was a dress rehearsal more than anything: "It was pretty cool to soak up the atmosphere and feel what it will be like in the final. The crowd was chanting GB, GB, a bit like Kiwi, Kiwi. It was electric out there all the way down [the course]."