Rome, Italy -- (Sports Network) - Newly-appointed world No. 1 Maria Sharapova and former top-ranked stars Serena Williams and Venus Williams were a trio of third-round winners Thursday at the $1.34 million Italian Open, a clay-court French Open tuneup.

The second-seeded Australian Open champion Sharapova got past Denmark's Caroline Wozniacki 6-4, 7-6 (7-3), while a fifth-seeded Serena drilled Italian wild card Sara Errani 6-4, 6-3 and a seventh-seeded Venus vaulted past 10th- seeded rising Russian Vera Zvonareva 7-5, 6-2 on Day 4 at Foro Italico.

Sharapova will become No. 1 when the newest rankings are released on Monday, following Justine Henin's stunning retirement announcement on Wednesday. It will mark the fourth time the Russian has ascended to the top of the rankings.

The 25-year-old Henin became the first-ever reigning women's world No. 1 to retire from the sport.

A big Day-4 upset came when French qualifier Alize Cornet cut down third- seeded 2007 Rome runner-up Svetlana Kuznetsova 6-2, 6-4. The U.S. Open runner- up Kuznetsova, of Russia, gave way to Serbian star Jelena Jankovic in last year's finale here.

A fourth-seeded Jankovic avoided an upset on Thursday by dismantling Russian Maria Kirilenko 6-1, 6-1.

In other third-round action, sixth-seeded Russian Anna Chakvetadze snuck past 12th-seeded Pole Agnieszka Radwanska 6-4, 1-6, 6-1, ninth-seeded Swiss Patty Schnyder overcame eighth-seeded Wimbledon runner-up Marion Bartoli, of France, 4-6, 6-4, 7-6 (9-7), and Bulgarian qualifier Tsvetana Pironkova was leading Victoria Azarenka 6-2, 1-0 when the Belarusian wild card retired with a left knee injury.

Friday's quarterfinals will pit Sharapova against Schnyder, Jankovic versus Venus, Serena against Cornet and Chakvetadze versus Pironkova. The Wimbledon champion Venus is playing her first tennis in a month after taking some time off for medical reasons.

Serena captured this Roman event in 2002, while her big sister Venus titled here in 1999 and was the runner-up in 1998.

This year's Rome titlist will collect $196,900.