The 37-year-old Serb lost the opening three games against America’s world number 43, but bounced back to take the first set on a tie-break.
Djokovic then stumbled with victory in sight, forced into another tie-break after letting a 4-1 lead slip in the second set, before finally seeing off 20-year-old Michelsen 7-6 (7-3) 7-6 (11-9).
The fourth-seed joins the ATP Tour’s top two players, Jannik Sinner and Carlos Alcaraz, in the third round following their wins earlier on Saturday.
“It was a first match against Alex and I also hadn’t played in a while, so it took me time to get the rust off,” said the 24-time Grand Slam champion, who had played just one Davis Cup qualifier since losing to Australia’s Alexei Popyrin at Flushing Meadows.
“He started terrifically. It was a very close encounter and I also thought it was a quite a high level of tennis.”
Michelsen had two points to take the match into a deciding set, including when serving at 9-8 up in the second-set tie-break, but unforced errors cost him.
Djokovic, who played with heavy strapping on his right knee, eventually capitalised on Michelsen’s mistakes to claim victory on his first match in China since 2019 as he bids for his 100th tour-level title.
