Who and when can change the current top 4?
1) Nadal. It's going to take an early exit from Wimbly and USO for him not to be 2009 World No. 1
2) Federer. He may drop to number 4 by the end of the year but he will be still clear of 5 and below.
3) Murray. Getting better by the match but still lacks the experience of defending major points; which he has to do later in the year.
4) Djokovic. Inconsistent in almost everything he does. Can't defend a title but will always do well when least expected.
Del Potro is the closest but he's possibly still a full year from challenging.
Wrong. Nadal will be number 1 even if those two things happen.