ROME - An aching Roger Federer made a seamless transition from slick blue clay to the slower red dirt on Wednesday as he saw off Carlos Berlocq of Argentina 6-3 6-4 to reach the third round of the Rome Masters.

The Swiss only decided to play after his morning practice session, carrying a few aches and pains following his Madrid Masters title win last weekend.

Second seed Rafa Nadal, beaten in the third round on the blue clay in Madrid, looked delighted to be back on the red stuff as he beat German Florian Mayer 6-1 7-5.

Adjusting from the slippery blue clay to the far slower red clay of the Foro Italico with ease, Federer conceded he had been unsure what to do up to the very last minute.

Roger Federer of Switzerland returns the ball to Carlos Berlocq of Argentina during their men's singles match at the Rome Masters tennis tournament May 16, 2012.[Photo/Agencies]

"I wanted to see how I felt and make sure that I didn't have anything major because we're ahead of a long summer," he told a news conference.

"If this was the last tournament of the season it would be no problem. But as this is the beginning of many tournaments in a row, potentially a lot of five-setters in a row, I need to make sure I make good decisions, so I go round by round.

"I'm happy that I felt OK out there today."

A good performance this week from Federer, who now plays former world number one Juan Carlos Ferrero, would help him to close the gap on Novak Djokovic in top spot.

Rankings talk  

"I might be world number three again next week but that doesn't matter for Rafa (the number three) and myself," he said.

"It's interesting times right now and I know there's going to be a lot of talk about the rankings.

"What I know is that I'll have a shot until the U.S. Open, whatever shape or form with the rankings, and we'll see how it's going to play. Right now I'm just happy I'm healthy."

Mayer beat Nadal the last time they played, in Shanghai last year, but on his favoured clay, the Spaniard never allowed him to really get a foothold in the match.

Rafael Nadal of Spain returns the ball to Florian Mayer of Germany during their match at the Rome Masters tennis tournament May 16, 2012.[Photo/Agencies]

"It is an important victory," Nadal said. "In the first set I played aggressively. Mayer put me in difficulty with his serve but I don't think I ever suffered."

Tomas Berdych, beaten by Federer in the Madrid final, eased past Lukas Kubot 6-4 6-1 to reach round three, while Juan Martin Del Potro also advanced.

In the women's event, Serena Williams made it two wins in the space of 18 hours as she battled back to beat Russia's Nadia Petrova 4-6 6-2 6-3.

Serena Williams of the US returns the ball to Nadia Petrova of Russia during their match at the Rome Masters tennis tournament May 16, 2012.[Photo/Agencies]

"When I saw the schedule, I said, 'Oh my God, are you serious," Williams said. "But that's life. You just have to be able to adjust and I was really happy I was able to come through."

Venus Williams improved her chances of making the Olympics on merit as she battled to a 7-6 6-1 win over Ekaterina Makerova of Russia.

The former world number one, who needs to climb above Varvara Lepchenko in the United States pecking order, will take on fifth seed Sam Stosur in round three.

There were defeats, though, for world number three Agnieszka Radwanska and former world number one Caroline Wozniacki.

Radwanska was ousted 6-4 4-6 6-1 by Petra Cetkovska of the Czech Republic while Wozniacki, suffering from sinus problems, quit when trailing 6-4 4-0 to Anabel Medina Garrigues of Spain.

Women's world number one Victoria Azarenka had no such problems, though, as she cruised past Shahar Peer of Israel 6-1 6-2 in the late match.