I agree General.
IF Rafa gets tired in the 3rd against Djokovic, it might not be as easy to come back into it against him.
That's why Rafa has to use these next few matches wisely.
If he feels he has the match in control, it wouldn't hurt him to stay out there a bit longer.
Then in the match before the QF, he should take it as easily as he can.
So even if Rafa looks and is stronger, his fitness in terms of endurance will have to be there against the likes of Djokovic, if they both make it to the QF.
Respectfully,
masterclass