Williams sisters both win in Rome

Having been pushed hard by Nadia Petrova, Serena eased through to the last eight with a 6-3 6-1 triumph over Anabel Medina Garrigues of Spain.

The ninth-seeded American has now won 16 matches on clay in a row, including picking up the title in Madrid last week.

Venus is also coming into form with the French Open looming large on the horizon, upsetting US Open champion and fifth seed Sam Stosur 6-4 6-3. The victory keeps her on target to play in this summer's Olympics in London.

Next up for Venus will be Maria Sharapova, the Russian having saved six set points in the first set on her way to a 7-6 6-3 triumph over former French Open champion Ana Ivanovic.

Petra Kvitova, seeded fourth in the tournament, also advanced with a 6-2 5-7 6-2 victory over Sorana Cirstea while China's Li Na and Italian Flavia Pennetta also reached the last eight.