#4 Juan Martin del Potro
It was unfortunate that the big Argentine had to sit out of the World Tour Finals due to an injury. The tournament would have been a lot more exciting with him in it.
However, he had a fantastic year - probably his best since coming back from his wrist injury. He performed consistently well at the Grand Slams apart from the Australian Open. He reached the semifinals of the French Open and the quarterfinals of Wimbledon, losing to Nadal in both matches. He went one step higher at the US Open, where he reached the final, only to lose to Novak Djokovic.
He won his biggest title of the year at Indian Wells where he defeated Roger Federer in the final after saving three match points.
He is currently recovering from his injury and will hope to get back to full fitness before the Australian Open.
Who Are Roger Federer's Kids? Know All About Federer's Twins