Sixth seed Eugenie Bouchard crashed out of the French Open in the first round on Tuesday but Serena Williams and Petra Kvitova are both through.
Canada's Bouchard, who reached last year's Wimbledon final, struggled to find her usual rhythm on Court Suzanne Lenglen as she lost 6-4 6-4 to France's Kristina Mladenovic.
Bouchard has only won three matches since February and the 21-year-old admits it is difficult to explain her sudden loss of form.
"I honestly don't know what to say," Bouchard said.
"It's been kind of the same as how I have been feeling recently on the court. Just not like myself.
"I definitely felt a bit better in Rome. I think that just makes it more disappointing to have a performance like today.
"So I just feel like it's been a while that this has been happening and it's unfortunate, but I'm sure one day it will stop."
Kvitova avoided a similar upset but it was far from comfortable for the fourth seed, who won 6-4 3-6 6-4 against New Zealand's Marina Erakovic.
"I have to say the conditions weren't really easy for me," said Kvitova, who will now face Spain's Silvia Soler-Espinosa.
"I think it was quite cold and the balls are really heavy, and they didn't really fly.
"For me it was really difficult to go for the shots. It was tough to make any winners.
"It was very difficult today. It was quite a long match and a big fight.
"Sometimes I couldn't win my serve so it was a little bit difficult but that's how it is in the first round of grand slams. I'm just glad I'm still in and still playing."
Williams is also through after she powered her way to a 6-2 6-3 win over Czech qualifier Andrea Hlavackova.
The American was dominant throughout, hitting five aces and 25 winners, and perhaps most importantly there were no visible signs of her troublesome right elbow causing her discomfort.
"I felt good," Williams said.
"I was really happy to get through that and see how my elbow was going to do.
"It was not 100 per cent, but I was able to serve okay, I didn't serve as many aces as I normally do. The good thing is it gets better every day.
"Another day off tomorrow and hopefully if I can win another round it would be better completely."
Caroline Wozniacki is also safely into round two after the fifth seed eased past Italy's Karin Knapp 6-3 6-0.
There were also victories for Russian veteran Svetlana Kuznetsova, America's Madison Keys and Italian Francesca Schiavone.