World number one Novak Djokovic has insisted that his refusal to underestimate Ryan Harrison was a large factor behind his convincing win over the American at the Australian Open earlier today.

Djokovic dropped just six games on the Rod Laver Arena as he set up a round-three meeting with Radek Stepanek.

Reflecting on his performance, the defending champion admitted that he had to be at the top of his game because his opponent had little to lose.

"I definitely didn't want to underestimate my opponent tonight, I still knew that he has a quality," said Djokovic. "Mentally he's probably going to go out on the court knowing he doesn't have anything to lose.

"He's going to try to smack serves and forehands. I went with that kind of mindset on the court, just trying to play as sharp as possible from the start, and I've done so."

Djokovic has won the title in Melbourne on three previous occasions.