It's 10 years since the rankings didn't feature either Rafael Nadal or Roger Federer in the top two, but current leading men, Novak Djokovic and Andy Murray, still face a test of clay-court nerve.

On Sunday, Nadal begins his bid for a ninth successive Monte Carlo Masters title.

The 26-year-old Spaniard, who was seven months out of action with a knee injury, has already hammered home his clay-court dominance in 2013 with comeback titles at Sao Paulo and Acapulco.