Ivanovic stunned in Rome

Top-seeded Serbian Ana Ivanovic has suffered her worst defeat of the season, upset 4-6 7-5 2-6 by Bulgarian qualifier Tsvetana Pironkova in the second round of the Italian Open.

And there was bad news for Australian tennis fans with Samantha Stosur joining Ivanovic on the sidelines.

Ivanovic, who was overtaken by Maria Sharapova as the world No.2 on Monday, had not lost to a player ranked lower than 33rd this season.

The world No.64, Pironkova had never beaten a top-five player prior to stunning Ivanovic. The 20-year-old, who has never won a WTA event, will face unseeded Victoria Azarenka in the third round.

Sharapova, who could soon regain the world No.1 ranking following the abrupt retirement of Justine Henin, defeated unseeded Slovakian Dominika Cibulkova, 6-2 3-6 6-4

Seventh-seeded Venus Williams survived the second round with a 6-4 6-1 triumph over unseeded Stosur.

The 27-year-old American - playing for the first time since missing a month with an undisclosed illness - improved to 16-3 at this event, which she won in 1999.

Her sister, fifth-seeded Serena Williams, also pushed into the third round with a decisive 6-2 6-0 win over Alona Bondarenko in just 62 minutes.

Italian wild card Sara Errani, who upset 11th-seeded Agnes Szavay, is up next for Serena.

Defending champion and fourth seed Jelena Jankovic won her second-round match with Flavia Pennetta, 6-1 6-4, to set up a meeting with unseeded Maria Kirilenko.

Last year's runner-up to Jankovic, third-seeded Svetlana Kuznetsova also eased her way into the third round with a 6-2 6-0 win against Olga Govortsova in 56 minutes.

The Russian will next face unseeded Frenchwoman Alize Cornet, who ousted 17th-seeded Francesca Schiavone 6-3 6-2.

Other seeded players through to the third round are number six seed Anna Chakvetadze, eighth seed Marion Bartoli, ninth-ranked Patty Schnyder, 10th seed Vera Zvonareva and No.12 seed Agnieszka Radwanska.

WTA Rome Masters, Italy
Tsvetana Pironkova (Bulgaria) def. 1-Ana Ivanovic (Serbia) 6-4 5-7 6-2
3-Svetlana Kuznetsova (Russia) def. Olga Govortsova (Belarus) 6-2 6-0
4-Jelena Jankovic (Serbia) def. Flavia Pennetta (Italy) 6-1 6-4
5-Serena Williams (USA) def. Alona Bondarenko (Ukraine) 6-2 6-0
6-Anna Chakvetadze (Russia) def. Kateryna Bondarenko (Ukraine) 3-6 7-6 (7-1) 6-0
7-Venus Williams (USA) def. Samantha Stosur (Australia) 6-4 6-1
8-Marion Bartoli (France) def. Virginie Razzano (France) 6-4 7-5
9-Patty Schnyder (Switzerland) def. Virginia Ruano Pascual (Spain) 6-1 6-0
10-Vera Zvonareva (Russia) def. Iveta Benesova (Czech Republic) 7-5 4-6 7-5
Sara Errani (Italy) def. 11-Agnes Szavay (Hungary) 6-0 6-3
12-gnieszka Radwanska (Poland) def. Roberta Vinci (Italy) 3-6 6-2 6-2
Alizé Cornet (France) def. 17-Francesca Schiavone (Italy) 6-3 6-2
Maria Kirilenko (Russia) def. Anabel Medina Garrigues (Spain) 6-3 5-7 6-2
Caroline Wozniacki (Denmark) def. Ekaterina Makarova (Russia) 6-3 6-4
Victoria Azarenka (Belarus) def. Monica Niculescu (Romania) 6-3 6-2

Postponed first-round matches
9-Patty Schnyder (Switzerland) def. Mariya Koryttseva (Ukraine) 3-6 6-2 6-3
Ekaterina Makarova (Russia) def. 13-Nicole Vaidisova (Czech Republic) 6-4 4-6 6-2
Maria Kirilenko (Russia) def. 18-Nadia Petrova (Russia) 3-6 7-5 6-4
Flavia Pennetta (Italy) def. Olga Savchuk (Ukraine) 6-7 (9-11) 6-3 6-1
Kateryna Bondarenko (Ukraine) def. Tathiana Garbin (Italy) 7-5 6-4
Alizé Cornet (France) def. Vera Dushevina (Russia) 6-1 6-3