Djokovic was looking increasingly agitated but Federer upped the ante in the last game and the NYC audience clearly wants him into the final. Federer did not play a great set but he is the one looking to make the winners
Federer is very up and down today, I thought he had cut this sort of crap out again. Djokovic has continued to maintain a consistent high standard and it may be the deciding factor in this match now it looks like it's going to a fifth set