KEY BISCAYNE, Fla. (AP) While Novak Djokovic is undefeated this year, Rafael Nadal remains the man to beat on clay.

Djokovic improved to 24-0 in 2011 when he beat Nadal on Sunday in the final at the Sony Ericsson Open, marking the end of the hard-court season to start the year.

Now the sport moves to clay, Nadal's best surface. During the spring clay season last year, the Spaniard went 22-0 and won four tournaments, including the French Open.

Nadal's reign on clay is the reason he's still ranked No. 1, even though he hasn't won a tournament since Tokyo in October. Djokovic is No. 2, but no one disputes he has been the game's best player in 2011 - so far.