Federer: I won't underestimate Soderling

Roger Federer claimed he will face an improved Robin Soderling when they meet again in the last eight on Wednesday.

Federer and Soderling set up a rematch of their 2009 Roland Garros decider by cruising through their respective last-16 matches.

Defending champion Federer came through a mid-match wobble to wrap up a 6-3 7-6 (7/5) 6-2 win over fellow Swiss Stanislas Wawrinka on Philippe Chatrier Court, while Soderling followed soon after thanks to an impressive 6-4 6-4 6-2 dismissal of 10th seed Mario Cilic on Suzanne Lenglen Court.

Federer has a daunting 12-0 record against the Swedish fifth seed, beating him at both Wimbledon and the US Open following last year's showdown in Paris.

But the world number one believes he may face a tougher Soderling than before.

"I think he's taken advantage of the better ranking he's had since the last year here," Federer said.

"I've never lost against him, so obviously that's a good record to have. But because of the improvements he's made, he's an opponent not to underestimate.

"He beat incredible players on the way to make the finals here last year, so clay seems to also become really his surface of preference, as well."

Soderling did manage to beat his nemesis in an exhibition match when they last squared off in January.

But Federer, 28, warned: "I don't want to downplay or up-play exhibition matches, but they're there to try out a few things.

"It's always better to win. But, at this stage of my career, I prefer to still try out a few things, because I'll have enough matches down the road where I can't try out too many things."

Federer has cruised into the last eight without dropping a set, while Soderling has surrendered only one.

The 25-year-old believes he has finally cracked the art of winning ugly.

"One or two years ago, I think I could play really good tennis," he said. "My highest level then was pretty much the same as now.

"But I'm winning more matches, and I think I'm winning more matches when I'm not playing my best tennis, which I didn't do so often before. That's the biggest change."

There was real drama on Philippe Chatrier less than an hour after Federer's win when Jo-Wilfried Tsonga was forced to retire from his match against Mikhail Youzhny through injury.

Eighth seed Tsonga, who was the last remaining French hope in the singles at Roland Garros, quit after losing the first set 6-2 in just 30 minutes.

The 25-year-old had been suffering pain related to a recurring back problem during his third-round win over Thiemo De Bakker and he revealed after quitting today that he was in similar discomfort.

"In my last match, I had trouble with my gluteal muscle," said Tsonga, who will have an MRI tomorrow to confirm the precise nature of his injury.

"Today, the first time I ran at the end of the first game - game ball for him when he hit a winning forehand - I blocked and I felt a sharp pain.

"Immediately after, I knew it was the same thing that I had felt in the previous match. It hurt even more."

Tsonga revealed he could have pulled out of the tournament yesterday but was determined to play today, though he admitted more rain and a postponement until tomorrow may have helped him.

"I thought that, of course, if it rained it wouldn't have been bad for me," he said.

"But it didn't rain, so I walked onto the court.

"I did not retire yesterday - walkover yesterday - because I wanted to stay in the tournament. For me, it was important.

"I fought, I tried to go to the end, even with a pulled muscle.

"Unfortunately now, I don't know exactly what is wrong with me."