Djokovic beat Federer at the Australian Open and Federer beat Djokovic at the US Open.
Djokovic is 27-6 on hardcourt this year while Federer is 18-6.
Djokovic has 2 titles on hard (Australian + Indian Wells) versus 1 for Federer (US Open).
Seeded opponents defeated on hard courts:
Djokovic has beaten Hewitt, Ferrer, Federer, Nadal twice, Cilic, Robredo, Roddick
Federer has beaten Berdych, Blake, Ljubicic, Stepanek, Djokovic, Murray
Edge: Slightly Djokovic
Hard court losses:
Djokovic has lost to Simon, Roddick, Federer, Murray twice, Kevin Anderson
Federer has lost to Simon, Roddick, Djokovic, Murray, Fish, Karlovic
Djokovic slightly over Federer. But it's close.