Serena steps up a gear on return in Rome

The world No 1 is playing her first tournament since winning the Australian Open in January, having missed the last three months with a knee injury.

Williams had made hard work of her first round win over Timea Bacsinszky but she looked more like her old self in taking the first set 6-2 against her German opponent. But a string of unforced errors from the American allowed Petkovic to get back into the match as she took the second set 6-3 to force a decider, only for Williams to keep her composure and cruise to a 6-0 win in the third set.

Her sister Venus, the fourth seed, also booked her place in the last eight as she claimed a hard-fought 6-3, 6-4 victory over Shahar Peer to leave the siblings on course to meet in the last four.

Jelena Jankovic was another seed to progress as she eased past Yanina Wickmayer 6-2, 6-0 with 14th seed Nadia Petrova defeating Alexandra Dulgheru 6-0, 3-6, 6-2.

Roger Federer, meanwhile, captured his first singles win of the season on clay by beating Bjorn Phau of Germany 6-3, 6-4 at the Estoril Open yesterday. The world No 1 conceded just 17 points on his service game as he rebounded from a first-round loss in Rome last week. "It was a very important match for me today," Federer said.

Federer, who had a bye into the second round at Estoril, will meet Arnaud Clement of France in the quarter-finals. The Swiss won the Estoril crown in 2008 but skipped last year's event.

The Rome Masters, where he lost against 40th-ranked Ernests Gulbis, was Federer's first singles match in nearly a month. He took several weeks off after losing in the fourth round at Key Biscayne at the end of March.

Fourth-seeded Albert Montanes, the defending champion, ousted fellow Spaniard Daniel Gimeno-Traver 6-1, 6-2 and next encounters eighth-seeded Pablo Cuevas. The Uruguayan overcame Marcel Granollers of Spain 7-6 (8), 7-6 (2).

Second-seeded Sorana Cirstea of Romania advanced in the women's event, triumphing 7-5, 7-5 over Michelle Larcher de Brito of Portugal.

Fourth-seeded Anabel Medina Garrigues of Spain and the seventh seed Peng Shuai of China also went through.