US open is the fastest slam surface at this point, so again, his top spin doesn't have the same bite there than it does at the French or the Aussie (maybe the balls play a part in that too, I don't know).

Also, Flushing comes at the tail end of a tough hard court season, not too long after the euro season...of course, Rafa can pick his spots in the US summer tour to avoid putting too much stress on his knees, but then he's going to be less prepared than the competition. The Aussie is different because it comes right after the longer winter break, everybody has three weeks or so to prepare at most, so it's a more level playing field.