top two players continue their rivalry at Roland Garros next week.
Federer slumped to his eighth dispiriting defeat on clay to the Spaniard in the Hamburg Masters final on Sunday, the worst possible preparation for the Swiss star as he gears up for another assault on the only Grand Slam title to elude him.
Nadal has won the last three tournaments in Paris, beating Federer in the 2006 and 2007 finals, and will be defending a perfect 21-match winning record at Roland Garros.
But the Mallorcan had to battle a hamstring strain in the first set of Sunday's final before going on to depose Federer as Hamburg champion winning 7-5, 6-7 (3/7), 6-2 after nearly three hours.
"I wish I could have won in Hamburg, that would have given me an even better feeling for Roland Garros," said Federer after his 10th loss on all surfaces to the Mallorcan.
"To have won here would have just confirmed that I am definitely playing well. I can definitely say I am feeling good, the three hours wasn't a problem, from the physical standpoint.
"But from Rafael's standpoint, he is perhaps struggling a bit more due to the stress with the levels of the last few weeks. I am completely fine and I will be ready for the tournament."
Nadal suffered blisters after winning the Barcelona final earlier this month against compatriot David Ferrer and could barely run at the Rome Masters where he lost to Juan Carlos Ferrero in the second round.
It was only his second defeat on clay since April 2005.
But he proved his fitness in Hamburg by beating world number three Novak Djokovic in the semi-final, before recovering from 5-1 down in the first set to beat Federer.
And despite suffering the hamstring problem, the Spaniard says he is confident of being fit to defend his Roland Garros crown.
"I am optimistic of playing Roland Garros, I will have to see how the leg settles down," said Nadal.
"The final (in Hamburg) was tough for me, especially after the hard semi-final, I felt a bit of pain in my hamstring and it was difficult to concentrate.
"But it helps to beat the world number one (Federer) and the best player this year (Djokovic), it's always important for confidence.
"The most important was to win Hamburg for the first time, regardless that it was the last event before Roland Garros."
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