There will be no goldck to become the first man to win all four majors and Olympic gold in the same calendar year, matching the feat Steffi Graf achieved in 1988.
But Djokovic will wonder what might have been after an astonishing collapse against world No.5 Zverev, losing 1-6 6-3 6-1.
“Tough day man, really tough day,” a visibly upset Djokovic told reporters.
“I feel so terrible right now. Can’t be positive right now.”
In Friday’s semi-final, an emotional Zverev embraced his opponent at the net, telling Djokovic: “I’m sorry”.
Zverev was in tears after he claimed 10 of the last 11 games to win, and was warmly congratulated by Djokovic at the net as the pair exchanged words.
“I told him that he’s the greatest of all time,” Zverev explained to reporters.
“I know that he was chasing history, he was chasing (the) golden slam.
“But in these kind of moments, we’re very close and we’re good with each other, so of course, I’m happy that I won but at the end of the day I also know how he feels.
“He won 20 grand slams so you can’t have everything.”
Zverev will take on Russian Karen Khachanov in the gold medal match.
Serbia’s Djokovic looked in complete control as he took the opening set with ease and broke for a 3-2 lead in the second to move to the verge of victory.
But Zverev immediately broke back to spark an eight-game winning run which levelled the match and put him in a commanding 4-0 lead in the decider and didn’t look back.
It is the third time Djokovic has lost in the Olympic semi-finals, with his only medal so far a Beijing bronze in 2008.
He still has a chance of gold at Tokyo, backing up in the mixed doubles semi-finals with Nina Stojanovic on Friday night.
He will face Spain’s Pablo Carreno Busta on Sunday in the bronze medal clash.
Djokovic had been on a 23-match winning streak taking in French Open and Wimbledon titles and had last suffered defeat two months ago when he lost the Italian Open final to Rafael Nadal.
Djokovic can still become only the third man to claim a calendar year grand slam if he wins the US Open which starts in a month’s time.
– with AAP