World number one Djokovic took just 31 minutes to claim the opening set of the match, running out a 6-1 winner.
Hewitt, who was the only remaining Australian left in the competition, responded positively in the second set but was unable to prevent his Serbian opponent from opening up a two-set lead with a 6-3 success.
The third set was a much tighter affair, with Hewitt battling back from an early break to level up the score at 3-3.
The former world number one held his nerve and at the fourth time of asking claimed the third set with a 6-4 win to take the match into a fourth set.
Both players traded serves early in the fourth, only for Djokovic to break to open up a 4-2 advantage, before going on to wrap up the match 6-1 6-3 4-6 6-3.
He will now take on Spain's David Ferrer for a place in the semi-final.