Caroline Wozniacki started having nightmares of being rolled off the New York City Marathon course in a wheelchair.
As first-time marathoners are supposed to, she had planned one long training run of close to the 26.2-mile distance. The only problem: The tennis star started winning too much in her day job.
That meant less time off and more fatigue. So going into Sunday's race, Wozniacki has never covered more than about 13 miles.
"I know that normally you should be doing more, but I've been playing so many long matches, and I think most people don't work out or play tennis for three, four or five hours a day," she said Wednesday.
"When I did half and I felt great, I thought, 'You know what? This is OK. I can finish this,'" she added.
Plenty of retired athletes have run marathons. The 24-year-old Dane knows of nobody who tried it in the prime of his or her career - and just a week after a grueling season ended.
On Saturday, Wozniacki lost in a third-set tiebreaker to top-ranked Serena Williams in Singapore in the semis of the WTA Finals. She then flew home to Copenhagen for a day before arriving in New York late Tuesday night.
"I think you need to be a little crazy, but in a good way, I hope," she said.
Wozniacki realized before Wimbledon in mid-June that this year's tournament schedule would allow her to do the NYC Marathon, a longtime goal. Always considered one of tennis' fittest players, she figured she could squeeze in enough extra running to add to what she already did in her tennis training.
The decision came less than a month after golfer Rory McIlroy broke off their engagement, timing Wozniacki has insisted was coincidental. The marathon plan could have distracted or wore her down. Instead, it seemed to improve her tennis.
Wozniacki started the season 15-9. Since her decision, she's 34-10, her ranking rising from 16th to eighth. She reached her first Grand Slam final in five years before losing to her good friend Williams at the U.S. Open on Sept. 7.
Still, other players don't seem to be clamoring to add marathon preparations to their tennis training.
Wozniacki's long stay at the Open left her just a week before back-to-back tournaments in Asia, and she advanced far in both. She started to panic that she wasn't fitting in enough running.
But after dropping her first match in Beijing, Wozniacki had three weeks off before the WTA Finals, opening up time to train. She was encouraged that her runs felt good - even if she never managed that long one.
"I thought I will save my energy and just get through with the crowd on Sunday," she said.
Her experience winning long matches leaves the former No. 1 player confident "I can push through anything."
"I think it's going to be mental more than physical," Wozniacki said.
She'll be accompanied by two pace-setters from Team for Kids, the charity she's supporting. The competitor in her has a time in mind, though she won't divulge it. Still, she plans plenty of waving to spectators and simply trying to finish.
Dismissing the risk of injury, she said that "as an athlete, you know your body so well."
"You know when you can push it," she added. "You know when you need to hold back."
Dr. Timothy Miller, co-director of the endurance medicine program at Ohio State, said that while the demands of tennis and distance running are very different, it's reasonable to think Wozniacki can finish. Some effective marathon training programs require only 30 miles a week.
The biggest risk of skipping that long run is Wozniacki can't predict how her body will react late in the race.
"You don't know what you'll have left the last five, six miles," said Dr. Miller, a marathoner himself who serves as a team physician for the Buckeyes.
Wozniacki always takes three weeks away from tennis at the end of the season. Her next tournament isn't until Auckland in early January.
She's received advice from one of her fitness coaches, who's an experienced marathoner, along with fellow player Kimiko Date-Krumm, who ran the 2004 London Marathon in 3 1/2 hours during her 12-year break from tennis. When Wozniacki went for a jog in Central Park two days after the U.S. Open final, fellow runners familiar with her marathon plans gave her thumbs-up.
Wozniacki is still mastering the art of drinking and running at the same time. Laughing, she acknowledged that "it goes all over the place."
Wozniacki has already raised more than $50,000 for Team for Kids, which helps fund marathon organizer New York Road Runners' youth programs. Andy Murray is among the tennis stars contributing.
"Serena, you're still missing," a grinning Wozniacki told the TV cameras at Wednesday's news conference. "No pressure. She asked me the other day where she could donate, and I gave her the website. ... Now I put her on the spot. So now she doesn't have a choice."