Jelena Ostapenko was left fuming after a "terrible day at the office" on Sunday, when she became only the second woman in the Open era to see a Roland Garros title defence end in the first round.
The Latvian served 13 double faults and made 48 unforced errors in an error-strewn display as she slumped to a shock 7-5, 6-3 loss to little-known Ukrainian Kateryna Kozlova on Philippe Chatrier Court.
The 20-year-old's performance was the total opposite of the scintillating attacking tennis that took her to the title 12 months ago.
"I think it was a terrible day at the office today for me," Ostapenko said.
"I mean, in general I played maybe like 20 percent of what I can play. Made like 50 unforced errors and so many double faults. Like couldn't serve today.
"Everything together just brought me a really bad result."
The fifth seed is only the sixth woman in the Open era to lose in the first round of a Grand Slam tournament as defending champion, after Steffi Graf at Wimbledon in 1994, Jennifer Capriati (2003 Australian Open), Anastasia Myskina (2005 French Open), Svetlana Kuznetsova (2005 US Open) and Angelique Kerber (2017 US Open).
Ostapenko said that she was hampered by a leg injury suffered during her quarter-final defeat by Maria Sharapova in Rome last week, and by a personal matter earlier on Sunday.
"It's more personal, but, just in general... Just woke up, you're like, your mood was not amazing, you just woke up and kind of some things went wrong, and then you are kind of pissed off, in the practice you're pissed off," she said.
"And then you go to the match and try to be positive, but everything goes not your way, and you still try to be positive, but then you lose the match and of course you cannot be positive anymore."
The French Open is the only Grand Slam event that begins on a Sunday, and Ostapenko felt that a later start would have helped her regain full fitness in time.
"I think if I was scheduled on Tuesday, I think Monday or Tuesday, at least one extra day would help me a lot, but unfortunately yesterday I didn't feel that I was in a great form."
- The opponent 'didn't matter' -
It was a third defeat in as many meetings with world number 66 Kozlova for Ostapenko, after previous losses at S-Hertogenbosch in 2016 and at an ITF event in Italy two years before.
But she insisted that her form was so poor that she would have lost no matter who she played.
"Any player who could hit like five shots back I think probably could beat me today because I didn't really play well and didn't really matter who was on the other side, because she was just waiting for me to miss," bemoaned the Latvian.
For Kozlova, this was the biggest win of her career, coming over two months since she feared she might need knee surgery after suffering an injury in Indian Wells qualifying in March.
She only returned to the court earlier this week in Nuremberg, and also needed medical attention after struggling with blisters on Sunday.
"Sometimes I have some blisters on the foot and I have this problem. And, yeah, it was ugly and disturbing me a lot," said Kozlova.
"But after medical time-out, yeah, the physio did a good tape. It helped me to survive."
Kozlova next faces either former world number one Victoria Azarenka or Katerina Siniakova of the Czech Republic for a place in the last 32.