Olympic bronze medallist Deena Kastor is expecting a tough challenge in her Boston Marathon debut on Monday.
The American, who won in London last year and in Chicago in 2005, takes on Boston holder Rita Jeptoo of Kenya and 2006 runner-up Jelena Prokopcuka of Latvia.
"I have come here with the goal of winning but I am in great company and it is going to be an all out fight," Kastor told Reuters on Friday.
Gale force winds and near-freezing temperatures are expected on Monday and could create the worst conditions since the race began in 1897, according to weather forecasters.
"There are three clear favourites but there could be others who are very close to them," said Amby Burfoot, the 1968 winner.
In the men's race, holder Robert Cheruiyot takes on fellow Kenyans Benjamin Maiyo, last year's runner-up, and Stephen Kiogora plus former winner Hailu Negussie of Ethiopia.
With no top American men racing in Boston this year, Meb Keflezighi will run in London a week later, the women's event is capturing all the attention.
Ranked the world number one marathon runner by Track & Field News, Kastor is creating the biggest buzz, not least because she was born in Newton on the race route.
Kastor said she prepared for Boston's hilly course by training on mountainous terrain.
"I know adverse conditions," she said. "I've gotten in training runs in snowy, windy conditions and in the rain."