The rookie professional joins Keiran Doe, of Auckland, and Gina Ferguson, of Christchurch, as the New Zealanders racing in the elite competition in the world's largest ironman-distance event.
The race has attracted 4500 to the start line, with more than 100,000 spectators expected to line the route.
In a Radio Wanaka interview yesterday morning, Greenwood (31) said she had been training full-time in Europe and had prepared as well as she could.
All she could do now was to keep her head clear.
"I have been familiarising myself with the course, which is quite twisty and turny, not like Wanaka, which is a lot of straight lines.
" I couldn't not be in better shape. I am looking forward to seeing what the body can do," Greenwood said.
Because she does not know very many of her competitors and is still coming to grips with coach Val Burke's new training regime, Greenwood is unsure what she can aim for and is focusing on performance and stage goals rather than an overall race goal.
The women's field is the toughest ever in Challenge Roth, and fireworks are promised in the competition between defending champion Yvonne van Vlerken, of the Netherlands, German star Nina Eggert and the popular Australian athlete Belinda Granger, who won the inaugural Challenge Wanaka race last year.
The men's race is also likely to be interesting, with many spectators interested in the fate of four-time Challenge Roth champion and reigning world ironman champion Chris McCormack (34), of Australia.
He won Ironman Germany last weekend in 7hr 58min 54sec, and his attempt at two long-distance races in one week is controversial.
Other elite men to compete include Luke Dragstra, of Canada, Chris McDonald, of Australia, Marc Pschebizin, of Germany, and Doe, who is coached by McCormack.
Tourism New Zealand, in association with Lake Wanaka Tourism, has arranged for five UK-based Maori warriors from Manaia to give New Zealand competitors a stirring welcome as they cross the finish line.
Manaia also performed at the Rugby World Cup.
