ROME-Top-seeded Ana Ivanovic was upset by Bulgarian qualifier Tsvetana Pironkova 6-4, 5-7, 6-2 Wednesday in the second round of the Italian Open.

Ivanovic struggled with her consistency and serving and never seemed comfortable on the red clay at the Foro Italico. She committed 59 unforced errors to Pironkova's 26.

"I felt quite flat out there and I found it a struggle to find my rhythm and to find something inside to fight," Ivanovic said. "I really struggled with my intensity today, and that obviously caused a lot of errors."

Ivanovic picked up the top seed in this clay-court warmup for the French Open when top-ranked Justine Henin withdrew citing fatigue. Henin announced Wednesday that she was retiring from tennis, effective immediately.

Ivanovic missed this tournament the last two years due to injuries. At the German Open last week, Ivanovic lost to Elena Dementieva in the semifinals.

The 64th-ranked Pironkova also beat Venus Williams at the 2006 Australian Open.

Both Williams sisters advanced Wednesday, as did No. 3 Svetlana Kuznetsova and defending champion Jelena Jankovic.

Fifth-seeded Serena Williams routed Alona Bondarenko 6-2, 6-0 and No. 7 Venus Williams overcame an early challenge from Samantha Stosur before beating the Australian player 6-4, 6-1.

Venus had been out for a month with an unspecified medical problem, which she would still not discuss in detail.

"I feel much better. I went to the doctor and got a lot of suggestions, and I went home and worked on it," she said. "I just worked very hard during that time that I was off the court with my fitness, and I think it's made a big difference."

Venus won this tournament in 1999 and was the runner-up in 1998. Her best result since then was a semifinal appearance two years ago.

Kuznetsova, last year's runner-up, routed Olga Govortsova 6-2, 6-0, and the fourth-seeded Jankovic beat Flavia Pennetta 6-1, 6-4 in the Italian's second match of the day.

Another Italian, Sara Errani, upset No. 11 Agnes Szavay of Hungary 6-0, 6-3.

Also, No. 6 Anna Chakvetadze defeated Kateryna Bondarenko 3-6, 7-6 (1), 6-0; No. 8 Marion Bartoli edged Virginie Razzano 6-4, 7-5; and No. 10 Vera Zvonareva beat Iveta Benesova 7-5, 4-6, 7-5.

Ninth-seeded Patty Schnyder, Maria Kirilenko and Alize Cornet each won two matches Wednesday because several from the first round were pushed back due to rain Tuesday.