By Sudipto Ganguly MELBOURNE (Reuters) – An exhausted and emotionally drained Rafa Nadal walked gingerly towards an exercise mat in the players’ gym at the Australian Open and collapsed on it in a heap. Hardly surprising given the 35-year-old had just spent five hours and 24 minutes on the Rod Laver Arena court, bathed in sweat, rallying from two sets down to edge out world number two Daniil Medvedev – an opponent 10 years younger. He may have had little left in the tank, but after a few minutes on the mat he picked himself up, got on his exercise bike and got on with his cool-down routine. “(…