Djokovic won with 3–0 (6–1,7–6(3),6–2) over the 19-year-old American Learner Tien.
The 38-year-old Serb has not played a match since he was eliminated in the semifinal against world number one Jannik Sinner at Wimbledon on grass in London on July 11.
On the women's side, the world number four, American Jessica Pegula, withstood the pressure and took home the victory in the first match of the tournament. She defeated the Egyptian Mayar Sherif with 2–0 (6–0,6–4).
For Djokovic's part, the qualifier Zachary Svajda, also from the USA, awaits in the next match, while Pegula will face the Russian Anna Blinkova.
