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]."
Meanwhile, Louise Ayling and Julia Edward could afford to be perplexed with their Olympic debut in the lightweight double sculls. The duo formed out of the Rowing New Zealand trials in March.
They finished third in their heat, forcing them into a repechage Tuesday night (NZT). They were beaten by Great Britain and Denmark, crews they had defeated in both World Cups during the European season. They secured silver and gold medals at those regattas in Lucerne and Munich, respectively, but pre-Olympic results can flatter to deceive.
Adding to their frustration will have been the slower times in the other two heats. New Zealand finished in 7.02.78, 5.81s behind Britain, while Greece won the second heat in 7m 03.66s and China won the third in 7m 15.57s.
However, little can be read into comparing heats. Conditions can change quickly and times alter accordingly.
The New Zealanders were the quickest through the first 500m, moved to second behind Britain over the middle 1000m before the Danes caught them towards the end.
"We were pleased with the start, happy with our boat speed through the middle but in the last 600-700m we may have gone a bit early trying to hold them [the Danes] off," Edward said.