The seven-times French Open champion's narrow loss to Argentine world No.73 Horacio Zeballos in Vina del Mar on Sunday was rightly regarded as a shock as Nadal's defeats on clay over the past eight years can be counted on two hands.
Even those rare reversals have come against players of the calibre of Roger Federer and most notably Novak Djokovic in 2011. The last time he lost to a player outside the world's top 20 on clay was five years ago in Rome when former world No.1 Juan Carlos Ferrero got the upper hand.
You have to go back to Palermo in 2004, before Nadal had won his first French title, to find the Spaniard losing to one of the game's journeymen, Frenchman Olivier Mutis who was then ranked outside the top 100.
Zeballos, who had never won a title before, played well but Nadal was clearly not firing on all cylinders despite reaching the final without dropping a set.
Worryingly for Nadal, he admitted the knee was still causing him pain.
"The knee is still bothering me, but you have to face adversity with the best possible face and look forward to keep working and enjoy what I like the most, to play tennis," world No.5 Nadal said.
"A week ago we didn't know how the body would respond. At least now I know we can compete at a certain level. I think that was a positive week.
"I was two points away from winning the title, but I said from first day that the result was not the most important thing, although I would've liked to win."