Djokovic appeared to be heading a for a comfortable victory until Hewitt battled back to take the match into a fourth set.
The Serbian eventually wrapped up the match, but he has credited Hewitt for the way he fought to stay in the encounter.
"I have to give credit to Lleyton, who never gives up, he's a great competitor," he said after his victory.
"For two sets and 3-0 I was playing really well and then suddenly I stopped moving, and I give a lot of credit for that to Lleyton."
Djokovic will now take on David Ferrer in the quarter-finals.