Fresh off a title in Madrid and back up to No. 2 in the rankings, Roger Federer showed off his strong form with a routine 6-3, 6-4 win over Carlos Berlocq of Argentina in his opening match at the Italian Open on Wednesday.

Seeking to win one of only three Masters 1000 events he's never claimed, Federer dealt well with the swirling wind inside the 10,500-seat stadium at the Foro Italico, coming to the net often to finish off points.

Federer won 18 of 23 points at the net and held a 24-13 edge in winners over the 38th-ranked Berlocq in their first meeting.

Rafael Nadal, who was replaced by Federer at No. 2 with his Madrid Open victory Sunday, beat Florian Mayer 6-1, 7-5 to get even for a defeat in his only previous meeting with the 28th-ranked German.

In women's action, top-ranked Victoria Azarenka routed Shahar Peer of Israel 6-1, 6-2 then announced she was withdrawing because of a right shoulder injury. Azarenka has won four titles this year, including the Australian Open. She lost the Madrid Open final to Serena Williams on Sunday.

Her withdrawal means her scheduled opponent Thursday, 14th-seeded Dominika Cibulkova, advances to the quarterfinals.

This tournament is the last major warm-up for the French Open, which begins May 27.

Earlier, Williams rallied past Nadia Petrova of Russia 4-6, 6-2, 6-3 to extend her winning streak to 15 matches, following titles in Charleston, S.C., and Madrid -- plus two wins in Fed Cup.

Serena's sister, Venus Williams, had an easier time reaching the third round, eliminating Ekaterina Makarova of Russia 7-6 (7), 6-1.

There were several upsets, with No. 3 Agnieszka Radwanska, No. 6 Caroline Wozniacki and No. 7 Marion Bartoli all eliminated.

Radwanska was beaten by 28th-ranked Petra Cetkovska of the Czech Republic 6-4, 4-6, 6-1; Wozniacki retired with upper respiratory illness while trailing Anabel Medina Garrigues of Spain 6-4, 4-0; and Bartoli was beaten 6-3, 6-1 by Julia Goerges of Germany.

Former French Open winner Ana Ivanovic routed Spanish qualifier Silvia Soler-Espinosa 6-2, 6-1 to set up a matchup with No. 2 Maria Sharapova.

On the men's side, Stanislas Wawrinka of Switzerland upset eighth-seeded Janko Tipsarevic 6-3, 6-1; and local hope Andreas Seppi of Italy eliminated ninth-seeded John Isner 2-6, 7-6 (5), 7-5.

Among those advancing were seventh-seeded Tomas Berdych, No. 10 Juan Martin Del Potro, No. 11 Gilles Simon and No. 12 Nicolas Almagro.

Federer has reached the final twice in Rome, losing to Felix Mantilla in 2003 and to Nadal in a fifth-set tiebreaker in 2006.

The win in Madrid moved Federer to No. 2 for the first time since March 2011 - although he's still seeded No. 3 this week.

"I look at the big picture and what is important to me is just to be in the top 10, and if I am No. 2 or not at the French Open doesn't change anything -- and it doesn't change anything for Rafa," Federer said. "That I was able to win Madrid was amazing, and that is what I look at right now -- not the rankings."

Federer considered skipping this tournament to stay fresh after playing a full week in Madrid, but said he decided to play "this morning after practice.''

With the top eight seeded players having first-round byes, it gave Federer an extra day off.

"At least here we have two days off, which can be a lifesaver," the 16-time Grand Slam winner said. "I don't think I would have played this tournament if I would have had one day off."

Federer next plays former No. 1 Juan Carlos Ferrero, the 2001 Rome champion.

Considering all the tennis Serena Williams has played during her streak, she didn't have much time after finishing her first-round win over Galina Voskoboeva near midnight Tuesday.

"It wasn't that easy. It was a quick turnaround," Serena said. "When I saw the schedule, I said 'Oh my God, are you serious?' That's life. You just have to be able to adjust and make the best of it and so I was really happy to come through today."

However, Serena appeared to struggle with her back at times.

"Everyone has aches and pains here and there and today I felt it a lot because I have been playing a lot and practicing even more," she said. "Hopefully I'll be better by tomorrow."

Williams next faces fifth-seeded Sam Stosur.

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