Unseeded Williams eased past fellow American Meilen Tu 6-2 7-5 and now meets France's Tatiana Golovin.
And the unseeded outsider took it 7-4 to reach round four for the first time.
Kvitova promptly lost in the first round of the U.S. Open to an unseeded opponent.
Ferrer's opponent Wednesday will be unseeded Jurgen Melzer, who rallied past Albert Ramos, 2-6, 6-3, 6-3.
Next up is the unseeded Ukrainian Dolgopolov following his shock victory over 2008 runner-up Tsonga.
She will meet fifth-seeded Conchita Martinez or unseeded 17-year-old Marta Marrero in an all-Spanish semi-final.
He has lost a set in each of his last three matches, despite playing unseeded opponents.
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Henin, unseeded in the season's first Grand Slam, edged the No. 19 seed Petrova, 7-6 (7-3), 7-5.
Azarenka's reward is a clash with unseeded German Anna-Lena Groenefeld, who beat Australia's Alicia Molik 6-4 6-4.
Matthew ended Mohd Azlan Iskandar's maiden run in the event, beating the unseeded Malaysian 11-2 11-9 11-10.
Veteran Tommy Haas , the No. 12 seed from Germany, beat unseeded Frenchmen Guillaume Rufin 7-6 6-1 6-3.
Clijsters will next face unseeded American Christina McHale, who had a 6-2 6-4 win over Japan's Ayumi Morita.
The Swiss maestro beat unseeded Finn Jarkko Nieminen 6-3 6-4 to successfully defend his hometown title in Basle.
Stephens was joined by two unseeded Americans reaching the round of 16 at Roland Garros for the first time.
She next plays unseeded Francesca Schiavone, the 2010 champion, who beat No. 13 Marion Bartoli of France 6-2, 6-1.
Sharapova, who was unseeded after injuries hit her world ranking, had her serve broken six times in the match.
Earlier, Russia's Nikolay Davydenko raced into the final after a comfortable 7-5 6-1 win over unseeded Martin Verkerk .
Unseeded Italian Alberta Brianti lies in waits for Stosur after she upset 21st seed Sabine Lisicki 2-6 6-4 6-4.
Current No. 1 Dinara Safina avoided any embarrassment with a 7-5 6-1 victory over unseeded Belgian Kirsten Flipkens.
The unseeded Clijsters is playing in her second tournament this season after four months out with a wrist injury.
Unseeded players are slotted into the draw by a computerized random number generator.
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The unseeded German reached her second final in two weeks with a 6-4 5-7 6-4 upset win against Dinara Safina.
The 2008 champion Ana Ivanovic is unseeded this year having dropped sharply down the rankings through poor form and injuries.
Her next opponent is unseeded Ukrainian Alona Bondarenko, who battled past Lucie Safarova of the Czech Republic 5-7 6-4 7-5.
Querrey, who beat unseeded Russian Igor Kunitsyn 6-3 6-4, is hoping to build on his L.A. Open title last weekend.
My third defeat was probably the hardest, when I lost to the unseeded Goran Ivanisevic after three rain affected days.
Federer will play unseeded Nicolas Kiefer in the last four after the German beat fifth seed Fernando Gonzalez 7-6 (7-5) 6-2.
Unseeded, she reached the last four at the US Open, having never passed the second round at any previous Grand Slam.
The Serb will now face unseeded German Tommy Haas, who defeated compatriot Philipp Kohlschreiber 2-6 7-6 7-6 in an epic encounter.
That would suggest a sizable edge except that seeded teams play away first and tend to be better teams than unseeded teams.
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