Kaia Kanepi of Estonia returns a shot during her third round match against Naomi Osaka of Japan on Day Six of the 2017 US Open at the USTA Billie Jean King National Tennis Center on September 2, 2017 in New York City (AFP Photo/Abbie Parr)

New York (AFP) - Not even the high-speed thrill of being one woman up against 33 men racing the treacherous ice drift roads of Finland could make Kaia Kanepi forget tennis.

Now, after almost two years out of action battling illness and debilitating injuries to her feet, the five-time Grand Slam quarter-finalist from Estonia is back in the big time.

Playing her first major since the 2015 US Open, the former world number 15 defeated Japan's Naomi Osaka 6-3, 2-6, 7-5 on Saturday to make the fourth round.

Not bad for the 32-year-old, who had to enter qualifying with a ranking of 418 and who had seen her sporting world collapse when she sat at home in Tallinn suffering the effects of Epstein-Barr virus and then painful plantar fasciitis in both feet.

"In June last year, I didn't care if I didn't play tennis again," said Kanepi.

"I needed a break from tennis and the longer the break the better."

Kanepi had already endured two lengthy absences from the sport through a back injury and an Achilles problem.

"I ignored the pain, kept playing tournaments, thinking it would go away," she said. "But it got worse and I couldn't play at all."

As she pondered what to do next, Kanepi walked her dog, Bossu, drove around Estonia to see friends and indulged her love of ice-road driving in Finland.

"It's great fun and very exciting," she said of her experience, in which she was the only woman taking part alongside 33 men.

"It's amazing. They teach you how to drive on ice. I like to slide but I don't know what the guys thought. They didn't say anything."

Kanepi also took a vacation in Hawaii at the end of last year and it was then that she decided she wanted to give tennis one more go.

So she underwent treatment on her feet and started training with Estonian 2008 Olympic discus thrower Gerd Kanter.

"I was his sparring partner. I was throwing a medicine ball, doing general fitness, although I didn't get to throw the discus," she said.

"I started training in January. I felt better and my heels weren't hurting anymore so I decided to try tennis again and it went on from there."

The US Open is just her fourth event of 2017 -- she won a second-tier ITF event in Germany and lost in qualifying at Wimbledon and Bucharest.

But Kanepi feels the omens are good for her at a venue where she made the quarter-finals in 2010.

On Saturday, she beat Osaka on Court 5 -- the same arena where she saved a match point to beat former champion Samantha Stosur in 2014.

"I feel like that's my court," she said. "It feels great to be back."