Novak Djokovic, back from the wilderness with an unlikely Wimbledon triumph, has even better tennis in him, Swiss great Roger Federer says. "I think he probably still has more left in him. I think he's playing well, but I think he can even play better," Federer said in Flushing Meadows ahead of the US Open.

Third-seeded Argentine Juan Martin del Potro also backed Djokovic to continue his rise back from a right elbow injury — all the way back to number one in the world. "I believe in him," del Potro said. "I know he has everything to win the first position in the world again.