Roger Federer lost to Borna Coric in straight sets, 6-4 6-4, in the Rolex Shanghai Masters semifinals match after an hour and 15 minutes. He awaits defending champion and top seed Roger Federer or Borna Coric of Croatia.
Djokovic, who had elbow surgery in February but recovered to win Wimbledon and then the US Open last month, said: "Being number two after this tournament is also a great achievement, considering the first four, five months of the year and considering I had the surgery".
Djokovic played his 1,000th career match against Zverev and holds an impressive 827-173 win-loss record.
"You can't write him off after beating Federer in this sort of manner", Greg Rusedski said of Coric on Sky Sports.
"He's really improved his game, stepping up into the court, goes for his shots more than he used to", Federer said of Coric.
The fourth seed, who is yet to win a Grand Slam despite his undoubted talent, angrily threw his racquet at the start of the second set as Djokovic ramped up the pressure. He squandered a first break point by firing a forehand into the net, but claimed the advantage on his second chance when his opponent shanked an bad forehand long.
Djokovic's serve has not been broken this week in 37 service games.
Serving for the match, Coric perhaps showed a first sign of nerves with a weak forehand into net to fall 15-30 down, but he responded with a big unreturned first serve, an ace and a forehand victor to send his illustrious opponent crashing out.
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Like Djokovic, the Croatian did not allow the Swiss maestro one break point opportunity during a comprehensive display.
"I think every year you feel more mature".
He will jump a spot to No 2 in the world if he reaches the final in Shanghai.
"That then plays a role for the rest of the season, and that's it, I still don't know".
Coric, world-ranked 19th, will face one of his toughest tests of the season against Djokovic in Sunday's showpiece.
"I was happy to get out in two", Federer said.
Djokovic posted only nine unforced errors to 24 for Zverev.
That run includes titles at the US Open and Cincinnati Masters. Coric won 84% first serve points to reach his maiden Masters 1000 final and book a fascinating clash against the Serb Novak Djokovic.