ROME (AFP) World number one Serena Williams overcame a mid-match slump to defeat unseeded Andrea Petkovic in three sets at the Foro Italico on Wednesday to reach the quarter-finals of the Rome Open. The Australian Open champion won 6-2, 3-6, 6-0 against the 49th ranked German but rarely looked to be at her best. And she was in relaxed mood after the match; having claimed on Sunday that she was cheeky and described her performance on Wednesday as rusty she said her adjective of choice for Thursdays quarter-final would be sexy. It went crazy in the second set. I started really well but then I was down and out in the second, she said. But thats the great thing about playing matches (rather than just training) and I was glad to win because youre guaranteed another match and I need it because you could see today I was rusty. However she insisted that she is already in better shape ahead of the French Open than she was last year when she lost in the quarters to eventual winner Svetlana Kuznetsova. Last year she lost in her opening match in three successive clay events leading up to Roland Garros. Im better than I was this time last year. I lost in the (second) round (after a first round bye) and wasnt doing so well. My goal is to do better than last year and so far its going well. She will play Russian Maria Kirilenko on Thursday after she beat Slovakias Dominika Cibulkova 4-6, 6-1, 6-1. One top name falling by the wayside was Danish second seed Caroline Wozniacki, who went down in straight sets 6-4, 6-2 to Spaniard Maria Jose Martinez while two more seeds also headed for the exit. Russian sixth seed Elena Dementieva lost out to former world number one Ana Ivanovic of Serbia, who advanced 6-1, 7-6 (7/5) while the Czech Republics Lucie Safarova put out Polish eighth seed Agnieszka Radwanska 1-6, 6-3, 7-6 (7/2). Serena is playing in her first tournament since winning in Melbourne in January but unlike her second round match on Tuesday when she started slowly, here she was out of the blocks quickly enough. She broke Petkovic in the fifth game with a backhand winner down the line and then again in the seventh with a cross-court forehand winner. Petkovic had not been overawed by her illustrious opponent, though, and was matching her for winners while Serena was producing as many unforced errors as the 22-year-old. Things got interesting in the second set as Petkovic broke Williams in the fourth game and had three break points for a 5-1 lead in the favourites next service game. Serena saved those, held and then broke back after Petkovic netted a forehand, a regular feature of her play. However, the German of Serbian origin then stepped up her game and made two outright forehand winners and a backhand winner on break point to move ahead 5-3. Serena had two chances to break back immediately but could not take either and she handed her opponent the set with a netted forehand. That seemed to focus her mind, though, and she romped through the final set with little fuss. Serena is still on course to meet sister Venus, the world number four, in the semi-finals after the elder Williams beat 16th seed Shahar Peer 6-3, 6-4. Venus, who has never dropped a set against Israeli Peer in four meetings, broke in the fourth game of the first set and went on to seal the set with a drive volley. She broke Peer again in the fifth game of the second set and it seemed as if victory was near but Peer broke straight back and even had two more break points on Venuss next serviced game. I think I got a little too relaxed, said Venus. Too tight is never good and too relaxed is never good but after that game I got my level up. But the five-time Wimbledon champion held serve, broke Peer with a forehand winner and then claimed victory on her second match point. She next plays seventh seed Jelena Jankovic after the former world number one thrashed Belgiums Yanina Wickmayer 6-2, 6-0.