Top seed Maria Sharapova edged through to the quarter-finals of the Bausch & Lomb Championships but second seed Anna Chakvetadze was knocked out.
Sharapova required two tie-breaks to defeat 15th seed Anabel Medina Garrigues of Spain 7-6 (7/3) 5-7 7-6 (7/1) to set-up a last-eight meeting with Alona Bondarenko.
Ukrainian Bondarenko defeated sixth seed Dinara Safina of Russia 7-6 (7/5) 0-6 7-5.
Chakvetadze, who was seeking her second title of the year after claiming her seventh career championship at the Paris indoors event in February, fell 6-2 3-6 6-1 to Slovakian Dominika Cibulkova in one hour 35 minutes.
Chakvetadze's erratic serving contributed to her downfall. The 21-year-old Russian recorded 11 double faults in her fifth defeat of the year.
American Lindsay Davenport defeated Croatian qualifier Karolina Sprem 6-4 3-6 6-4 to advance.
Sprem had beaten third seed Daniela Hantuchova in the previous round, but Davenport prevailed in one hour 49 minutes after converting 27 out of 39 first-serve points and recording eight aces.
The 31-year-old Davenport, who has won the title here three times, in 1997, 2004 and 2005, and improved her record to 33 wins from 38 contests in 10 appearances.
Eighth seed Agnes Szavay of Hungary awaits Davenport after a 3-6 6-2 6-3 win over Katarina Srebotnik.
The only other former champion here, 11th seed Amelie Mauresmo moved within a win of her first semi-final of 2008 after defeating seventh seed Agnieszka Radwanska 3-6 7-5 7-6 (8/6).
The 28-year-old Frenchwoman, who won here in 2001, had been lost all four meetings against top 30 players this year prior to beating the 16th-ranked Pole.
Unseeded Alize Cornet and 13th seed Virginie Razzano also have advanced and will meet in an all-French quarter-final.
