Clark entered the Waimakariri River with a lead of little over two minutes, an advantage he had turned into a 14 minute edge over Hunt by the midway stage.
South African Robyn Owen was a comfortable women's winner, going one better than her runner-up finish in 2017.
She finished well clear of Kiwis Sophie Hart and Simone Maier.
Former two-time winner Hart made some headway over the closing stages in her return to the race following a five-year hiatus but she couldn't close the enormous gap forged by Owen.
Defending champion Elina Ussher finished further back, the 41-year-old denied what would have been a record-equalling fifth win.
- NZN
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