(CNN) -- Holder Svetlana Kuznetsova has been dumped out of the French Open at the third round stage, beaten in three sets by fellow-Russian Maria Kirilenko.
Sixth seed Kuznetsova -- who had to save four match points when scraping past Germany's Andrea Petkovic in her second round match -- was beaten 6-3 2-6 6-4 by her 30th-seeded compatriot.
However, Kuznetsova was philosophical about her defeat. She told reporters: "You cannot play great all the time. It's up and downs.
"I haven't been playing well this season. It happens and I'll be back. It's just a matter of time," she added.
Kirilenko will now meet 17th seeded-Italian Francesca Schiavone for a place in the quarterfinals.
Meanwhile, both the Williams sisters, who are seeded to meet in the final, progressed with straight sets victories.
With the sun finally shining at Roland Garros, top seed Serena took just 55 minutes to beat Germany's Julia Georges 6-1 6-1 in a second round match postponed from Thursday.
The world number one will now play Russian 29th seed Anastasia Pavlyuchenkova for a place in the last 16 on Saturday -- as the American bids to lift the trophy for the first time in nine years.
Venus has already secured her place in the last 16 thanks to a 6-3 6-4 win over Slovakia's Dominika Cibulkova, the 26th seed.
The elder Williams sister is joined by third seed Caroline Wozniacki and 14th seed Flavia Pennetta in the fourth round.
Dane Wozniacki cruised to a 6-3 6-4 success over Romanian 31st seed Alexandra Dulgheru and will now face Italian Pennetta, who secured a 6-3 6-0 victory over Slovenia's Polona Hercog.
And Russian fifth seed Elena Dementieva is also through to the last 16, but she had to recover from dropping the opening set to defeat Aleksandra Wozniak of Canada 6-7 6-3 6-4.
Elsewhere, four-time champion Justine Henin, who is playing in her first French Open since 2007, needed just four games to complete a 6-3 6-3 win over Czech Kara Zakopalova to set up an intriguing third round tie with a resurgent Maria Sharapova.
"It's going to be very exciting to play her again in my second career," 22nd-seed Henin told the official WTA Web site.
"She's a real fighter. She remains someone very, very strong. She has the fighting spirit. It's going to be a question of attitude and trying to be aggressive. I want to win the match tomorrow."
Russian 12th seed Sharapova has been struggling with an elbow injury this season but overcame another Belgian Kirsten Flipkens on Friday, and will now face Henin for the 10th time in her career.
France's best hope for a female champion, 13th seed Marion Bartoli, also had to finish a match left over from Thursday against compatriot Olivia Sanchez. Bartoli progressed easily to the third round 7-5 6-2.
Another outside favorite for the title, seventh-seeded Australian Samantha Stosur, made it through to the third round with a hard-fought 6-4 1-6 6-0 victory over Paraguay's Rossana de los Rios.
Belgian 16th seed Yanina Wickmayer, who beat France's Sybille Bammer 7-5 in the final set, will now play Slovakian 23rd seed Daniela Hantuchova, who beat Olga Govortsova in straight sets.