Flustered champion Jelena Ostapenko falls at first French Open hurdle

A flustered Jelena Ostapenko became only the sixth female Grand Slam champion to fall at the first hurdle of her title defence on Sunday. (Reuters)

A flustered Jelena Ostapenko became only the sixth female Grand Slam champion to fall at the first hurdle of her title defence on Sunday when she lost to Kateryna Kozlova at the French Open.

Never at ease on the Roland Garros main show court, the world number five slumped to a 7-5 6-3 defeat to a Ukrainian opponent who had won both the pair`s previous meetings.

Not since Anastasia Myskina went down in the opening round of the 2005 tournament has the French Open lost its women`s champion so early, and the 20-year-old slipped off court, her head bowed, ruing what she called a "terrible day".

By losing, Ostapenko joins an ignominious group including, as well as Myskina, Steffi Graf, Jennifer Capriati, Svetlana Kuznetsova and Angelique Kerber who all lost as Grand Slam champions on the first run of their defences.

Kozlova, competing with a large, weeping blister on her heel which caused her to take a medical break at the end of the first set, was well worth the victory, playing with power and composure, in contrast to the flustered champion.

"Obviously, it feels great... I didn`t expect anything from the match. I just went to enjoy every moment on the court because, before, I was not sure if I will be able to play in [the] French Open," Kozlova said, citing a knee injury which had sidelined her.

"So I was just happy to be on court, back on court, and compete. So it was very important for me. And, in the end, the result comes up and it`s just amazing."

Amazing for Kozlova, dismal for Ostapenko, whose eyes searched the coach`s box at every opportunity.

Last year, she had lit up Paris by lifting the title with an exciting, powerful style and smiling, jaunty demeanour.

Where in 2017 she made a habit of coming back from the dead to win seemingly lost matches, this year she showed little grit.

She seemed unable to find any answers to the questions Kozlova was posing, and checked out early with barely a whimper.

"It was terrible day," she told reporters afterwards, her pink cap pulled low over her eyes.

"Honestly today began not in a nice way and I knew something like that could happen, so I tried to stay positive. But...

"I just woke up here and my mood was not amazing. [A] few things go wrong and you are pissed off, but you try to stay positive. Then you lose a match, and it is no longer possible to be positive."

Ostapenko said she might have had a better chance had she been scheduled on Monday or Tuesday but that it had simply not been her day on Sunday.

"When I went on court today I had this unbelievable pressure, and felt I was not myself on court."

"I will just try to forget this as soon as I can."

It might appear lower-ranked players are becoming something of an Achilles` heel to the Latvian - already this year she had lost to two players outside the world`s top 50. Kozlova, ranked 66, makes it an unhappy hat-trick for the 20-year-old.