Top seed Ana Ivanovic of Serbia crashed out of the Italian Open in her first game, losing 6-4 5-7 6-2 to Bulgarian qualifier Tsvetana Pironkova.

Former world number one Venus Williams beat Australian Samantha Stosur 6-4 6-1 while her sister Serena also joined Pironkova in the third round with a resounding 6-2 6-0 win over Ukrainian Alona Bondarenko.

Serbian defending champion Jelena Jankovic, the fourth seed, progressed in straight sets too with a 6-1 6-4 victory over Italy's Flavia Pennetta.

Ivanovic made an untidy start with too many groundstrokes finding the net or going long and she soon went down a break, but she broke back in the ninth game only to fail to hold immediately after and concede the set.

The world number three twice surrendered a break advantage in the second set and let a string chances to take the Bulgarian's serve again go begging before she finally managed to level things up.

But the unforced errors kept flowing and she was broken three times on the way to losing the decider.

"I felt quite flat out there and I found it a struggle to find my rhythm and find something inside to fight," Ivanovic said.

"I really struggled with my intensity today and obviously that caused a lot of errors. It's something I have to work on. Now I have 10 days to prepare for the French Open".

Seventh seed Venus Williams, returning from over a month on the sidelines with an unspecified medical problem, was put to the test immediately against Stosur and lost her serve in the opening game.

She broke back in the eighth game and cruised after that, breaking Stosur again to take the first set before dominating the second to set up a match with Russian 10th seed Vera Zvonareva, a 7-5 4-6 7-5 winner Czech Iveta Benesova.

Fifth seed Serena Williams, who like her sister Venus is a former Italian Open champion, will meet Sara Errani in the next round after the Italian wildcard crushed Hungarian 11th seed Agnes Szavay 6-0 6-3.

Pennetta struggled to compete with the fourth seed Jankovic after taking three sets in the morning to beat Ukraine's Olga Savchuk . That match, like those of the Williams' sisters, was postponed from Tuesday because of rain.

Reuters