Federer never displayed the same kind of stamina that Nadal displayed at Wimb this year. At 31, Fed had nothing left in the tank in the Olympics final after playing 4.5 hours against Delpo, while Nadal at 32 had no problems playing 5 hours against Djokovic after having already played 5 hours against Delpo.
Hmm, 2011 French Open final.
Federer: he was getting tired throughout the 3rd set and also the 4th, unfortunate I couldn't take my chances.
Nadal was extremely tired in the US Open 2011 final too, you could see it in the 4th set after that marathon 3rd set he had emptied his tank, actually both players were tired in that 4th set but Djokovic just had little bit more than Nadal. Nadal was also lucky in the 2009 AO final as Federer mentally collapsed in the 5th because Nadal looked tired from the middle of the third set onward and Federer had a ton of chances to win that set and he would have won it in 4 if he had won that set. There have been quite a few occasions when Nadal has looked tired, 2017 AO final is another one, you could see he didn't have the same zip in his shots in the 5th set. He usually doesn't show it like most other players and keeps his body language positive, kind of complete opposite of Del Potro , who looks tired from the first set.
Of course, Nadal has excellent conditioning, but so do Federer and Djokovic. When was the last time Federer actually looked tired in a match? He is 5-6 years older than both of them.