watched the match and Haas really played well - also he was hitting a lot of on-the-line shots (i assume he would miss then on a normal day), and more importantly returning a lot of serves well - djokovic won only 50% of 1st serve points (he served 64% 1st serves in).
Djoker, on the other hand, was not constructing points well, making tons of really UEs, and serving a lot slower than usual. Wind, cold, or not - those unforced errors were just unbecoming of him.
He had a chance to get back into it, but again poor serving and point blank UEs were causing him to lose his last serve game in 2nd set.
I am a Nole fan, and have to say that he deserved to lose. It seem like Haas wanted it more and was more focused (like with JMDP @ IW)
His level has dropped drastically since Dubai (exception being that Tsonga QF at IW). I trust this is just a phase, which all players go through from time to time.