Then a dominant performance against Karen Khachanov in the final.
The fifth-ranked German earned Olympic gold in style.
Zverev overwhelmed Russian opponent Khachanov 6-3, 6-1 at the Tokyo Games on Sunday for the biggest title of his career.
"This is so much bigger than anything in the tennis world -- in the sports world," Zverev said.
The 6-foot-6 Zverev controlled the match with his big serve and a confident two-handed backhand, never really giving the 25th-ranked Khachanov a chance.
Zverev's previous best performance was reaching the final of last year's U.S. Open, where he wasted a two-set lead in a five-set loss to Dominic Thiem.
"There is nothing better than this," Zverev said. "You're playing for everybody involved. This is not only for yourself; this is for everybody."
IOC president Thomas Bach watched his fellow German win the title as a group of about 10 anti-Olympic protesters across the street from the Ariake Tennis Park made themselves heard inside center court. Play was not interrupted.
"We all heard it. It was quite loud," Zverev said.
It's been quite a run for Zverev, who also dominated in the final two sets against Djokovic.
Besides serving six aces, Zverev also showed his touch with a delicate topspin lob winner midway through the second set.
Combined with a series of backhand winners from Zverev that landed just inside the lines, Khachanov grew frustrated to the point that he slammed a ball high into the mostly empty stands between serves with Zverev ahead 5-0 in the third.
While the heat was again a factor with the temperature at 90 degrees and a heat index of 99, Zverev finished off the match so quickly -- in 79 minutes -- that it didn't really make an impact.
When it was over -- after a big serve out wide on his first match point led to an error from Khachanov -- Zverev went face-down on the court and cried.
Zverev joined Steffi Graf as the only Germans to win gold in singles, with Graf having won in 1988 when she achieved the Golden Slam by winning all four Grand Slam titles and the Olympics in the same year.
Djokovic also had a chance at the Golden Slam -- until his loss to Zverev.
Djokovic also lost the bronze-medal match to Pablo Carreño Busta of Spain on Saturday.