McEnroe feels picking a winner between Novak Djokovic and 13-time French Open champion Rafa Nadal is like a coin toss but he gives Serbia's world number one a slight edge in Tuesday's highly-anticipated quarter-final. Spaniard Nadal had won the French Open four years in a row before losing to eventual champion Djokovic in the semi-finals last year - just the third time he had been beaten at the claycourt major since his debut in 2005. That was also the last of the 58 career showdowns between the pair and Djokovic has looked in peak form at this year's tournament, having not dropped a set in his four rounds.