Who can beat Djokovic ?

Lleyton Hewitt played at his best in todays Australian Open 4th round, but Djokovic stayed cool and just played his strong, effortless game without becoming emotional or stressed. Though he had to concede one set to Hewitt, he never let the target out of sight. He is simply to strong now, and neither
Federer nor Nadal is playing up to what Djokovic does right now. I believe only DelPo can beat him in this tournament..on a very bad day for the Serb.
The thriller in the quarterfinals will be DelPotro against Federer, which I predict to be a very tough match where the man with the clearest head will be able to hang in there to take the victory. Ferrer shows a strong game now, too, and I think he has a small chance to beat the big surprise from Japan, Nishikori, to reach the semi finals. The hardest part is not to guess who will become champion, but who is going to be the runner up in this years Australian Open. I favour Nadal or DelPotro to become Djokovic` prey in the finals.
See highlights here:
http://australianopen.com