Anastasia Potapova pulled off the biggest shock on day one of the French Open by dispatching Angelique Kerber and Elina Svitolina sent Venus Williams packing in Paris.
Kerber had been out of action since suffering an ankle injury at the Madrid Open and the fifth seed's hopes of completing a career Grand Slam were ended when world number 81 Potapova consigned her to a 6-4 6-2 defeat.
Svitolina has been hampered by a knee problem, but the WTA Finals champion claimed her first clay-court victory of the season when it really mattered - seeing off veteran Williams 6-3 6-3.
Garbine Muguruza, the 2016 champion at Roland Garros, fought back to beat Taylor Townsend 5-7 6-2 6-2 on Sunday.
Karolina Pliskova and last year's runner-up Sloane Stephens were among the other winners on the opening day, while Svetlana Kuznetsova was knocked out by the 203-ranked Kristina Kucova a decade after winning the title.
NO EXCUSES FROM KERBER
Kerber had only played three matches on clay this season prior to Roland Garros due to her ankle injury.
"This is not my excuse. I tried my best," said Kerber following her surprise defeat to 18-year-old Russian Potapova. "I know there is still a little bit of work to do to really play matches at 100 per cent, to slide, to jump on the foot, and on the leg."
Potapova was elated to pull off a first victory over a top-10 opponent on her French Open debut against a player she looks up to.
"I was really looking forward for this match because I like [Kerber] very much. She's actually one of my idols, and when I was young I was looking for her game, how she's playing," she said. "When you step on the court and you play your idol, you've just got to show your best. That helped me."
SVITOLINA BACK FROM BEING 'AWAY WITH THE FAIRIES'
Svitolina has not had the season she had would have wanted after winning the WTA Finals, but hopes a win against Williams will be the start of a resurgence.
"Sometimes in a few matches in the past two months, I had a situation where I was not thinking about what I had to do on court. I was more away with the fairies, I would say," said the ninth seed.
"So, it's not easy, but I learned a lot during these two months, and I tried to have a right mindset, which is going to help me to handle this.
"Today it was a good example that I can do it and I took my chances."
MUGURUZA TOWN BUT NOT OUT, STEPHENS AND PLISKOVA THROUGH IN TWO
Muguruza was a semi-finalist last year after winning her maiden major at this tournament three years ago, but she was in danger of making an early exit at the hands of Townsend.
The 19th seed raised her game to topple the American, hitting 37 winners to seal her spot in round two.
Second seed Pliskova defeated Madison Brengle 6-2 6-3, while Stephens was a 6-3 7-6 (7-4) winner in her encounter with Misaki Doi.