The 39-year-old Serb won the first set in a tiebreak, 7–6 (7–3), and was a game down in the second set when the Australian was forced to retire.
It was not the first time Djokovic won the tournament without the match being completed.
In the semi-final against Daniil Medvedev, the Russian was disqualified after hitting a spectator in the face with the ball.
"A bit of a shock," Novak Djokovic said at the time.
Djokovic remains undefeated in Beijing, where he has won all 34 matches in the seven tournaments he has played.
Djokovic is the greatest men’s player of all time, with 24 Grand Slam titles.
