The Serbian beat American Alex Michelsen in a thrilling two-set match that finished 7-6 (7/3), 7-6 (11/9).
Meanwhile, Jannik Sinner and Carlos Alcaraz showed why they were top in the world as they raced through to the next stage with confident straight-set wins.
Sinner dispatched Japan’s Taro Daniel 6-1, 6-4, while Alcaraz made short work of China’s Shang Juncheng, winning 6-2, 6-2.
Four-time Shanghai champion Djokovic did not have it easy against 43rd-ranked Michelsen.
Introduced as the “Greatest Of All Time” as he walked onto the court, he received a rapturous welcome from the packed stadium.
But Michelsen started the first set strongly, breaking Djokovic early and going 1-4 up –- to the displeasure of the crowd, fully behind the 37-year-old former world number one.
To their delight, the Serbian levelled, and then hit his stride in the tiebreak, winning it 7-3.
The reverse happened in the second set when it was 20-year-old Michelsen’s turn to catch up to take it to the tiebreak.
Novak Djokovic admitted to being “surprised” by Michelsen
Novak Djokovic admitted to being “surprised” by Michelsen.
“It took me a little bit of time to get the rust off and to start feeling better on the court,” he said.
“I was very glad to keep calm when it mattered in both tiebreaks.”
The crowd, already in a frenzy after Novak Djokovic spoke Mandarin at the end of the match, went wild as he showed off a new trick — attempting a sentence in the Shanghainese vernacular.
World number one Sinner has said he is not in a “comfortable” situation thanks to a World Anti-Doping Agency (WADA) appeal against a decision by tennis authorities to clear him of wrongdoing after he twice tested positive for a steroid in March.
His recent blistering winning streak was broken by Alcaraz in the China Open final on Wednesday.
But there was no tiredness on display from either player on Saturday, with 23-year-old Sinner looking completely unruffled in the first set against the 93rd-ranked Daniel.