Juan Martin del Potro
No. 258 to No. 11
Del Potro's ranking actually bottomed out at No. 485 in January. Of course, the 2009 U.S. Open champion's plummet was due to a wrist injury. He didn't play for nine straight months in 2010. But by April 2011, he was back in the top 50. Del Potro won two tournaments this season and pushed Novak Djokovic and Rafael Nadal to four sets at the French Open and Wimbledon, respectively.