2 days ago he just played a brutal 4 set fight vs. Brands in 40 degrees temperature. Less than a week ago he played 5 top 50 players and beat all of them. So yes, at 20 years old, being tired after such a strong perfomance against a vintage Fed in the first 2 sets, its only normal and human.
Ok, but playing back to back tough matches is what the Big Boys do all the time, and those that are in tip top condition rebound more quickly than those who are not.
A well conditioned athlete in tip top condition would have no problem recovering from matches played over a week ago --- so the Sydney campaign is irrelevant, in my opinion.
And regarding the Brands match which had a day of rest before the Federer match, it lasted less than 3 hours --- 40 minutes 1st set, 46 for the 2nd, 36 for the 3rd, and 53 for the 4th. That's a total of 175 minutes, 5 minutes shy of 3 hours. Not particularly difficult at the elite level.
In a Grand Slam, the top 10 players all can easily play a 3 hour match, have a day of rest, then easily come back to play another match and not be tired after 90 minutes.
The Big Boys want to win the Slams and they train for exactly the very long and demanding back-to-back matches that often happen in the Slams. They train to play a 5 hour match in hot conditions on day 1, have a day of rest, then play another 5 hour match in hot conditions on day 3. They train for the most grueling circumstances
to outlast the less conditioned opponent. That is why they are Grand Slam champions.
Bernie needs to do this regularly in training if he wants to win more that an occasional fluke Slam. It seems he hasn't gotten this memo yet.