PARIS, France - The latest swerve in her career's learning curve might turn out to be nothing more than a bump in the road for Latvia's Jelena Ostapenko.

The 20-year-old became just the second woman in the Open Era to fall in the first round of her title defense at the French Open on Sunday, as she crashed out to Ukrainian World No.67 Kateryna Kozlova.

Read more: Kozlova KOs defending champ Ostapenko in Paris shocker

"I think it was terrible day at the office today for me. I mean, in general I played maybe like 20% of what I can play," Ostapenko said after the match.

"I made like 50 unforced errors and so many double faults, and couldn't serve today. Everything together just brought me a really bad result. I had this unbelievable pressure. I felt that I'm not myself today on court.

"The day began not like in a nice way and I knew that something like that can happen but I was trying to be positive and to think positive, but in the end I couldn't really do that."

Ostapenko waves goodbye to the fans on Court Philippe Chatrier. (©Jimmie48/WTA)

Having lost to Kozlova in each of their previous two meetings, Ostapenko looked out of sorts for the duration of the one hour and 34 minute encounter.

The No.5 seed struck 48 unforced errors and 13 doubles faults, as she served at just 47% for the match and was broken seven times.

The Latvian later confessed that her preparation to defend her first career title was less than ideal after suffering an injury in a quarterfinal defeat to Maria Sharapova at the Internazionali BNL d'Italia in Rome.

That match, following Anastasia Pavlyuchenkova's defeat of Dominika Cibulkova in the final in Strasbourg on Sunday, is the fourth-longest on the WTA this year. 

"After Rome I was injured so I didn't really play for, like, four days. I just played a couple days before the match today, and I think that was not enough," she said.

"When I played against Maria, I did a split and I got injured, and then when I went back home I went to see the doctor. I tried to recover my leg as soon as I could but unfortunately I didn't feel that great today."

Ostapenko, the first Grand Slam singles champion from Latvia, joins Russia's Anastasia Myskina in tournament infamy. The Russian lost her first match at the 2005 French Open to María Sánchez Lorenzo after she was also the first woman from her country to win a Grand Slam singles title.

"I'm really disappointed and so angry. I mean, I'm, just, like really angry and I just want to turn back time," she said. "When I went on court today, I was, like -- I had this unbelievable pressure, because the fans, they were supporting me a lot and I really wanted to play and to show them that I fight."

The Latvian made 48 unforced errors in defeat. (©Jimmie48/WTA)

Even Kozlova knew what was weighing on the defending champion, while she won her third straight match against Ostapenko.

"I know that if I will play her game, that's what she wants, and I'm trying to play differently, and probably this is the reason [for the 3-0 head-to-head]," said Kozlova. "But this match is different, of course. She had so much pressure."

The Latvian's fight will just have to take a different form in the coming days instead.

While her singles campaign came to an end on Sunday, Ostapenko won't be leaving the City of Lights just yet - she and Elena Vesnina are set to be the No.10 seeds in the doubles draw.

"Of course there are another tournaments and another opportunities," she said. "If you always remember you lost first round in a Grand Slam, then I think you have to finish your career. I will just try to forget it as soon as I can, and I'm still playing here in doubles. 

"I think the pressure should be over, because I had to defend a title here, and the grass court season, I have to do a good preparation and then just, yeah, just enjoy the season."