Caroline Wozniacki vowed to fight back and stay positive after her latest setback at the French Open.
Former world No. 1 Wozniacki, a major champion in Melbourne just last year, was the 13th seed at Roland Garros amid a difficult season so far, having retired in the first round at both the Madrid Open and the Internazionali d'Italia.
The Dane was able to complete her opener on Court Philippe Chatrier on Monday, but the outcome was no more positive against Veronika Kudermetova.
Wozniacki looked to be on course to a comfortable win early on but collapsed to a 0-6 6-3 6-3 upset, later explaining to the media that a calf injury had disrupted her preparation on clay.
However, the 28-year-old was optimistic that she would now be able to build towards the grass season and Wimbledon.
"My calf now feels good, so that's a positive," she said. "And I'm definitely going to go back and just practice and work hard and get ready for the grass season.
Another day, another upset!
— Roland-Garros (@rolandgarros) May 27, 2019
Veronika Kudermetova fights back to topple Wozniacki 0-6 6-3 6-3.#RG19 pic.twitter.com/zvqNgUn5YJ
"It's definitely frustrating. You want to win, you're competitive, you work hard, and you want to see results. It hasn't been a great year for me so far and I'm just going to try to work hard and try to turn that around. Right now, there's not much I can do about the first six months of the season.
"I had some good weeks where I felt great, and then I've had some weeks where I've been sick and some weeks where I've been injured.
"I just have to try to stay positive. Obviously it's not as easy to stay positive when things aren't going your way, but I think that's when you really need to just keep grinding."
Kudermetova now will face either Kazakhstan's Zarina Diyas or France's Audrey Albie in the second round.