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The United States-based pro-race rider made her charge at the halfway stage of the eight-lap 123km event on the Cashmere/Hoon Hay course and won in a time of three hours 38 minutes 19 seconds.
National series champion Serena Sheridan of Hawke's Bay pipped defending champion Rushlee Buchanan of Te Awamutu in a sprint finish to claim second, 1min 13sec adrift of Cheatley.
A swirling easterly wind made conditions testing for the field, especially on the seven ascents of the gruelling Dyers Pass Rd, making Cheatley's solo ride even more impressive.
"Sometimes I ask myself why I do this but if I'm finding it hard so is everyone else," Cheatley said.
The presence of her husband and father inspired the 27-year-old and with not a lot happening in the first part of the race she made a break early "and gritted my teeth and put it all out there".
Cheatley said she had felt terrible at first but with hill climbs her strength she had gradually got into the groove and began to feel more comfortable. She decided to make her break early because there wasn't a lot happening at the back of the peloton. She said she is excited to be taking the national jersey to the US this year and will wear it "with pride".
Sheridan, who was "stoked" with second place, said she and Buchanan had worked hard over several laps to rein in Cheatley.
"But Cath's a real powerhouse. She was incredible today -- no-one can touch her at the moment."
Buchanan, 22, said it had been a tough race and she believed she had given her all to clinch third place.
Another fancied rider, Kaytee Boyd, 32, part of the strong Waikato Bay of Plenty contingent was fourth, 3min behind Cheatley while new national time trial champion Sonia Waddell was 12th.
Commonwealth Games silver medalist Jo Kiesanowski of Canterbury withdrew from the event last night because she believed it would be too strenuous when she is joining the New Zealand track team in camp tomorrow to prepare for this month's Beijing leg of the World Cup series.
The championships conclude tomorrow with the men's race on the same course, with 12 laps over 187km.