PARIS  - Serena Williams and Maria Sharapova, two players better known for their hardcourt and grasscourt abilities, are the form players going into the climax of the claycourt season at the French Open.

Between them they won the four main leadup events on the surface at Charleston and Madrid for the American and at Stuttgart and Rome for the Russian.

The question is whether one of them can sustain their form through two weeks and seven matches in the often unpredictable playing conditions that are a mark at the famed Roland Garros complex on the western edge of Paris.

Williams, whose only win here came 10 years ago when she defeated sister Venus in the final, has staged yet another impressive return to form in recent weeks.

The 30-year-old defeated Lucie Safarova in the final at Charleston before pounding world number one Victoria Azarenka 6-1, 6-3 to take the Madrid Open title at the start of May.

She subsequently withdrew from the semi-finals of last week's Italian Open with a lower back injury but has expressed confidence she will be fully fit to challenge for the title in Paris.

On top of that she has re-dedicated herself to her sport following the nightmare she went through with injuries and illness in 2010-2011.

"I think in general I have much better commitment in tennis. I just am really 100%," the 13-time Grand Slam champion said.

Sharapova, at 25, is a late convert to claycourt tennis having once described her movement on the slippy red dirt surface as being "like a cow on ice".

She reached the semi-finals last year before losing to eventual champion Li Na and it was the Chinese player she defeated last weekend to defend her Italian Open crown in Rome.

She also chalked up a straight sets win over Azarenka in the final at Stuttgart, a win that followed losses to the Belarussian in the finals at the Australian Open and Indian Wells. But her only encounter so far this year with Serena Williams resulted in a 6-1, 6-3 thumping in the quarter finals in Madrid.

There is also the question of whether Sharapova's notoriously inconsistent serve can survive through two weeks of outdoor conditions with gusts of wind whipping up the dirt particles and causing all sorts of havoc.

The Russian though is quietly confident that she has a realistic chance of completing her career haul of Grand Slam titles having previously won Wimbledon and the US and Australian Opens once apiece.

Of her play on clay she said: "It's always nice to come to Roland Garros knowing that I have been playing extremely well on it and having won a few titles in the last few weeks."

Defending champion Li, who last year made history in Paris by becoming the first Asian player to win a Grand Slam singles title, showed in her run to the Rome final, where she stretched Sharapova to a third set tie-breaker, that she is running into form at just the right time and could challenge again.

Azarenka, however, seems to have stalled after a tremendous start to the year that saw her win four tournaments, including the Australian Open, and rise to number one in the world rankings for the first time.

She will be the top seed in Paris but there are injury doubts following her withdrawal from her third round match in Rome with a shoulder injury. She has also has been troubled by a wrist injury.

The east European challenge could also come from Wimbledon champion Petra Kvitova of the Czech Republic and the consistent, but lightweight, Agnieszka Radwanska of Poland, while US Open champion Samantha Stosur of Australia and 2010 French Open winner Francesca Schiavone of Italy both have the games to go deep at Roland Garros. Since Laver's 1969 achievement, only Pete Sampras, Roger Federer and Nadal have had opportunities to complete a non-calendar year Grand Slam.

Sampras lost to Jim Courier in the quarter-finals at Roland Garros in 1994; Federer lost to Nadal in the final at the 2006 and 2007 French Open while Nadal lost to David Ferrer in the quarter-finals at the 2011 Australian Open.  Djokovic defeated Nadal in the finals of Wimbledon, the US Open and this year's epic Australian Open to arrive at his date with destiny.

Until the start of the claycourt season, he had also beaten Nadal in a total of seven successive finals. But world number two Nadal has since defeated the Serb on clay in the finals in Monte Carlo and Rome.

Roland Garros remains the only major where Djokovic has yet to make the final.

Three times the 25-year-old has been a semi-finalist, losing to Nadal in 2007 and 2008 before seeing a remarkable 43-match winning run ended by Federer at the last-four stage in 2011.

Ten-time a Grand Slam title winner, Nadal, 25, has a remarkable CV at the French Open -- six trophies in 2005, 2006, 2007, 2008, 2010 and 2011 -- and a match record of 45-1.

His only blip, a 2009 fourth round loss to Robin Soderling, came at a time when he was plagued by the acute knee problems which have often threatened to overwhelm him.

This season, Nadal has, once again, been supreme on clay and arrives in Paris boasting a 16-1 record on the surface.

But the Spaniard is keen to play down talk of a seventh French Open.

"I have much more than I ever dreamed," said Nadal. "I am coming here every year with the motivation to play well. But I am not going to be more motivated because I have six and I can win seven.

"The motivation always is the same -- sometimes you lose; sometimes you win. That's sport and that's the game."

Despite his 31st birthday fast approaching, and with the last of his 16 Grand Slam titles won at the 2010 Australian Open, there is little indication of Federer losing his powers.

The Swiss world number three was the man to benefit when Nadal slumped to his stunning 2009 loss in Paris, taking his first and only French Open title.

This will be his 14th French Open appearance. After making his debut in 1999, it took until 2006 for him to reach his first final -- the first of three successive title match defeats to Nadal.

After ending Djokovic's winning run in the semi-finals last year, he fell to a fourth final loss to his great Spanish rival.

The Swiss took the Madrid blue-clay court title -- one of four trophies this year -- and cruised through the Rome Masters until he ran into Djokovic in the semi-finals.

And Federer believes Djokovic will be thwarted in his attempt to make history.

"Rafa is the favourite for me," said Federer. "He's playing for his seventh title, so no discussion. We're crazy to even talk about this. Some people might say he's not the favourite, but to me he's the favourite."

World number four Andy Murray heads into the French Open, where he lost to Nadal in last year's semi-final, with question marks over his fitness after he revealed that he has been carrying a back injury since December.

His claycourt season has reflected his physical frailities -- quarter-final exits in Monte Carlo and Barcelona followed by a third round loss in Rome.

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