Ivan Ljubicic, one of Nadal's haters in the past, told SSSports of Italy today morning that he saw Nadal limping in his practice session yesterday. Nadal signing autographs in the end tells everything. So I don't think he lost any confidence with this defeat. It is just a casual cost he pays once in a while to be able to win more grandslams going forward.
I think he will come out relaxed at the US Open and surprise everyone with his tennis. Mind you he already won the only hardcourt tournament he played this year, Indian Wells.