Third seed Venus Williams was taken to a deciding set by fellow American Bethanie Mattek-Sands before eventually sealing her place in the second round of the French Open.
Clay is comfortably Williams' least favourite surface and she has only progressed beyond the quarter-finals once at Roland Garros, when she lost the 2002 final to sister Serena.
She claimed a 6-1 4-6 6-2 win over Mattek-Sands to clinch a second-round meeting with either Lucie Safarova or Sabine Lisicki, but was again far from convincing on the dirt.
The same cannot be said for Dinara Safina, the top seed and world number one who looked a player at the top of her game in her 6-0 6-0 thrashing of Britain's Anne Keothavong.
Safina, the tournament favourite, wrapped up the match in 61 minutes and was delighted with her form ahead of a clash with fellow Russian Vitalia Diatchenko.
‘I came on the court expecting a tough game because she had been playing well,’ said Safina, who hit 24 winners.
‘But I started to play and I felt good. I think I played a solid game.’
On her status as the woman to beat this year, she added: ‘I'm not really paying attention to what people are saying.
‘The most important thing is to play my game and take it day by day, match by match.’
Other seeds to advance on the second day of action were China's Jie Zheng and Hungary's Agnes Szavay.
Zheng, the 15th seed, eased past France's Stephanie Cohen-Aloro 6-1 6-3 and Szavay, the 29th seed, beat Corinna Dentoni 6-3 6-4.
One seed to fall today was Alisa Kleybanova (23), the Russian going down 6-2 4-6 6-1 to Polona Hercog, of Slovenia.
Cohen-Aloro's defeat added to the reverses suffered yesterday by five French women, one of them being 16th seed Amelie Mauresmo.
Other home players to be knocked out today were Camille Pin and Stephanie Foretz, to Tamarine Tanasugarn and Kirsten Flipkens respectively.
Aravane Rezai reversed that trend by thrashing Japan's Ai Sugiyama 6-3 6-2.
