The Serb won the match 6-3 3-6 6-3 against his Argentine opponent to seal his 19h consecutive win since losing in the US Open final.
With the score at 3-2, Djokovic took control of the first set when he broke his opponent at the fifth attempt, before going on to win 6-3.
Djokovic started the second set slowly and Del Potro won a break point in the sixth game to take a 4-2 lead, as he went on to level the scores.
In the third set at 1-1, Del Potro had two break points against Djokovic but the Serb came back to hold his serve.
The miss proved costly and Djokovic eventually broke him at 4-2 and from there he went on to wrap up the set 6-3.