By Martyn Herman
(Reuters) - Say it quietly but some chinks are appearing in the suit of armor Rafael Nadal usually wears on a claycourt as the Spaniard sets his sights on a ninth French Open title.
By his high standards the 28-year-old Spaniard has suffered a mediocre season on Europe's red dust courts so far and one or two players, chiefly Novak Djokovic, will arrive in Paris with genuine title hopes.
World number one Nadal has lost three matches on his beloved clay in the build-up to Roland Garros for the first time in a decade while others he normally sweeps aside on the surface have pushed him mighty close.
Fellow Spaniard David Ferrer, the man he beat to become the first man to win a single grand slam eight times last year, surprised him in Monte Carlo, then he lost to compatriot Nicolas Almagro in Barcelona and last weekend he was overwhelmed by Djokovic in the Italian Open final.
Even his 44th career title on clay, achieved in Madrid, earlier this month, was not totally convincing as he was outplayed for a set in the final by Kei Nishikori before the Japanese player retired with back problems.
That said, the alarm bells will not be ringing yet in the Nadal camp ahead of the grand slam which begins on Sunday.
Roland Garros remains a fortress for Nadal where he has suffered only one defeat since winning the title on his debut in 2005. Swede Robin Soderling is the only man to beat Nadal there and his record is an astonishing 59-1.
Beating him over five-sets on clay has proved almost impossible and once he gets into his stride on Paris's relative fast and bouncy claycourts he appears unstoppable.
Djokovic got to the brink of victory last year in a spellbinding five-set semi-final lasting four and a half hours after which Nadal explained that he "enjoyed suffering" the kind of physical punishment dished out by the Serb.
The scars build up over the years, however, and Nadal now looks more vulnerable to the kind of attacking onslaught the likes of Djokovic, Australian Open champion Stanislas Wawrinka, Andy Murray when he is in the mood and Nishikori can unleash.
Nadal is still the bookmakers' favorite to prolong his reign in Paris and can be relied upon to raise his level a notch or two over the next fortnight.
"I feel good physically. I'm feeling better and better physically, better than a year ago," Nadal, who has appeared untroubled by his suspect knees this year, said.
"This is the most important thing. Mentally I am still excited about what I'm doing. It still makes me happy. I still feel fortunate that I am doing what I'm doing."
Djokovic, who is closing in on Nadal in the ATP rankings, is also fighting fit after a wrist injury scare that forced him to miss the Madrid Masters this month.
The Serb was imperious in Rome, coming back from a set down to dominate Nadal in the final as he beat his great rival for the fourth time in succession.
"Winning a final of a great tournament with Rafa on clay is definitely an ultimate challenge," Djokovic, bidding to complete his career grand slam, said after his Rome triumph.
"I am very happy with my game and I hope I can carry it to the Roland Garros."
Roger Federer, who will arrive in Paris with double the amount of children he had 12 months ago after fathering a second set of twins, would dearly love to double his French Open title haul.
The 32-year-old Swiss, who briefly interrupted Nadal's domination in Paris when winning the title in 2009, has produced some stunning form this year, silencing those who had written him off as a fading force.
He beat Djokovic in Dubai and Monte Carlo and Murray in Australia and will believe he can better his quarter-final run last year when he was beaten by French hope Jo-Wilfried Tsonga.
Murray, who has slipped to eighth in the rankings, will be hoping for a kind draw but could find himself up against Djokovic or Nadal in the quarter-finals.
The Scot, still without a coach after parting with Ivan Lendl, played his best match of the year when losing narrowly to Nadal in the Rome quarters.
"I think I've got a good opportunity to do well in Paris," the 27-year-old Wimbledon champion said.
"I missed it last year and that was a very tough one, so I'm looking forward to going back."
Having won the title in Barcelona Nishikori, 24, looks the best bet among the young guns to make an impact having begun to consistently live up to his billing as a potential Asian superstar to rival China's Li Na on the women's side.
American Michael Chang, who won the French Open as a 17-year-old in 1989, is now working with Nishikori and believes he is close to a major breakthrough.
"He has been making good progress and has gained a lot of confidence and belief in his game and it's starting to show," Chang told the South China Morning Post.
"Winning a grand slam is certainly a possibility."
(Reporting by Martyn Herman)