TOKYO—With his Golden Slam bid over for at least another three years, Novak Djokovic rested his head on Alexander Zverev’s shoulder as his German opponent and friend consoled him. “I told him that he’s the greatest of all time,” Zverev said. “I know that he was chasing history.” Djokovic, the top-ranked Serb who had seemed invincible in all of the biggest tournaments this year, lost to Zverev 1–6, 6–3, 6-1 Friday in the semifinals of the tennis tournament at the Tokyo Olympics. Djokovic was attempting to become the first man to win all four Grand Slam tournaments and Olympic gold in the same year. He won the Australian Open, the French Open and Wimbledon this year and needed the Olympic and U.S. Open titles to complete the Golden Slam collection. Steffi Graf in 1988 remains the only tennis player to achieve the Golden Slam. “He won 20 Grand Slams,” Zverev …