ROME — The Williams sisters reached the quarterfinals of the Italian Open on Wednesday.

Top-ranked Serena Williams, playing her first tournament in three months, defeated Andrea Petkovic of Germany 6-2, 3-6, 6-0. Venus Williams also advanced, with a 6-3, 6-4 win over Shahar Peer of Israel.

The sisters are back from knee injuries, and could meet in the semifinals after being placed in the same half of the draw.

Serena Williams had been off the tour since she won the singles and doubles at the Australian Open, and was a wild-card entry in Rome. Her game was erratic at times against the 49th-ranked Petkovic and she had almost as many winners as unforced errors, 25 to 21.

"I definitely felt extremely rusty today," Williams said. "I'm glad I was able to win because at least I can be guaranteed another match. I think I definitely need it."

She got off to a good start, winning the first set with a five-game streak. But she quickly fell 4-1 behind in the second, came back to lead 4-3 but conceded another decisive break to Petkovic. In the third set, Williams picked up her game and played aggressively.

She next plays Maria Kirilenko of Russia, who defeated Dominika Cibulkova of Slovakia 4-6, 6-1, 6-1.

Williams said that after three months off she needs to stay healthy and play some matches. That's why she decided to skip social events at home and in favor of playing the clay-court event in Rome.

She told herself to "forget Oprah and Anna Wintour" — co-chairs of the Metropolitan Museum of Art's annual Costume Institute Gala Benefit on Monday in New York.

"I was supposed to be there. I had a fabulous dress," Williams said. "It hurt me. ... I wanted to really be there, but this is my career and I need the extra match."

The fourth-seeded Venus Williams, sidelined with a knee problem since losing the Key Biscayne final, broke once in the first set and dropped just four points on her serve. Both players then lost serve early in the second, and Venus had to save two break points at 4-4 before getting the decisive break in the next game with a forehand winner.

She saved another break point when serving for the win before converting her second match point.

Venus Williams will next take on Jelena Jankovic, who was impressive in rolling to a 6-2, 6-0 victory over Yanina Wickmayer of Belgium.

The Serb ousted Venus Williams in the 2008 quarterfinals on her way to her second Rome title.

Also, Nadia Petrova of Russia won 6-0, 3-6, 6-2 against Alexandra Dulgheru of Romania, who knocked out defending champion Dinara Safina on Tuesday.