They swam, cycled and ran in a gruelling 113km race - and at the finish, an Aussie emerged as Auckland's Half Ironman.
In the final 21km run of the event, Australian athlete Tim Reed outpaced his opponents to finish in 3h 49m 53s, 30 seconds ahead of compatriot Leon Griffin.
New Zealand veteran Cameron Brown, a 10-time Ironman New Zealand champion, came in third ahead of five-time world champion Craig Alexander in fourth.
With its exclusive championship status, the event carries 50 qualifying slots for the 2015 Ironman 70.3 world championship in Austria.
Athletes had to complete a 1.9km Viaduct Harbour swim, a 90km bike ride over the Auckland Harbour Bridge and a 21.1km run along the waterfront to finish at Wynyard Quarter.
New Zealand's Gina Crawford managed second place in the women's race, behind American Meredith Kessler.
Ironman racer critically ill
A competitor in yesterday's Ironman 70.3 race in Auckland was in a critical but stable condition last night after he came off his bike.
The incident occurred on Constellation Drive, on Auckland's North Shore, but last night an Ironman spokesman said he did not know why the man had fallen off.
It is understood the accident caused other cyclists to come off their bikes also.
Last night, a spokesman for Auckland City Hospital said the man, in his 40s, was in a critical but stable condition.
The gruelling half-ironman event, part of a worldwide series, involved a 90km bike ride, a 1.9km swim and a 21.1km run.
Australian Tim Reed took out the men's event in a time of 3h 49.53s.
American Meredith Kessler won the women's race in 4h 20.12s.