"Definitely wasn't the best match I've ever played," said the 13th-seeded Wozniacki.
Wozniacki's record this year dropped to 9-8 after her fourth straight loss -- including first-round defeats in Madrid and Rome -- since reaching the final of a clay-court event in Charleston, South Carolina, last month.
Wozniacki, 28, announced in October that she has rheumatoid arthritis.
The match marked Kudermetova's debut in the main draw at Roland Garros and the biggest win of her career in terms of ranking. The Russian player hit a whopping 40 winners to Wozniacki's 15.
Wozniacki's preparation for Paris had been hampered by an injured left calf, which was heavily wrapped Monday, but she said that was not an issue against her 22-year-old opponent. The Danish player also said she was not bothered by her rheumatoid arthritis, an autoimmune condition that can cause pain and swelling in the wrist and other joints.
"I played really well in the first set. I played aggressive. I played the way I wanted to play. And then I think she got very lucky at the start of the second set and took advantage of the opportunities she got," Wozniacki said, her chin resting on her left hand. "And then I think I just lost a little steam in the end."
She made only three unforced errors in that opening set, but 18 over the last two.
Wozniacki's results have not been the sort she is accustomed to. She made it to the quarterfinals and the fourth round in Paris in the last two years.
"You want to win, you're competitive, you work hard and you want to see results. So, it hasn't been a great year for me so far. And I'm just going to try and 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," Wozniacki said.
"I just have to try and stay positive, and 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 -- and you need to just keep grinding."