Seems like from 3-0 onwards in the 3rd set, he deliberately gave Hewitt games to make sure he lost a set and also lose the -9.5 spread.
No doubt that Hewitt played unbelievable and full credit to him for keeping balls in play but still Djoko should have been able to handle Hewitt with ease.
It could very well have been the heat BUT this guys is a pro.
Things I noticed:
* He stopped attacking on most points. As Jim Courier mentioned, he stopped dominating on his forehand, he started playing slice backhands etc
* He stopped chasing alot of balls in the 3rd set. From Djoko's standards, there were at least 10 easy returns that he drilled into the net or long. This never happens.
* He showed almost no emotion when his serve was broken, almost like he was expecting to lose it. At the same time even when he broke Hewitt in that 4th set, it seemed like he didn't care.
* There seemed to be 2 different Djoko's at the end. One that constantly made unforced errors, and one that won games with ease when he wanted to. Take the last 2 games as an example. At 5-2 up in the 4th set, Djoko barely even tries to return Hewitt's first serves. And when the ball is in play, it seems like Djoko is deliberately hitting balls with more air hoping to hit it long. Once Hewitt covered the 9.5, have a look at Djoko's service game, it was all business. A couple of aces and a couple of winners that looked effortless. The contrast in his game was very apparent to me.
All in all, just a very bad beat. Sometimes these things happen but it just seemed very odd.