Novak Djokovic has been invincible so far this year but his assault on Rafa Nadal's world number one ranking could be about to hit the skids.
At least that is what common logic suggests as the claycourt swing begins as the nine-times major winner Nadal has never lost to Djokovic on clay.
Djokovic's surge to second in the rankings on the back of a 24-0 start to 2011, including the Australian Open title and victories over Nadal to claim the Indian Wells-Miami double, means Nadal is under pressure to repeat his 22-0 stampede through last year's claycourt grind.
Nadal still leads Djokovic by more than 3,000 points in the world rankings but the 24-year-old has 5,000 to defend over the next eight weeks or so, culminating in the French Open before trying to retain his Wimbledon crown on grass.
