By Rozanna Latiff and Sudipto Ganguly
TOKYO (Reuters) - Beating Novak Djokovic is currently the toughest job in tennis but Germany's Alexander Zverev hopes his best will be enough on Friday to halt the Serb's march towards a Golden Slam when they meet in the semi-finals of the Tokyo Olympics.
World number one Djokovic is three-fifths of the way to winning all four Grand Slams and the Olympic gold in the same calendar year - the so-called Golden Slam.
He needs the singles gold medal in Tokyo and then the U.S. Open title to become only the second player to achieve the feat that German Steffi Graf accomplished in 1988.
The 24-year-old Zverev has defeated Djokovic twice in eight meetings - the last time at the 2018 ATP Finals.
Asked what it would take to beat Djokovic on Friday, Zverev told Reuters: "My best tennis. Like he's the favourite but I know that. There's very few guys that can beat him in the world and hopefully I can be one of them.
"I know I've done it before, I know that he is playing the best tennis of his life, but hopefully tomorrow I can show my best tennis as well."
Fourth seed Zverev played at a high level in his quarter-final against Jeremy Chardy on Thursday, beating the Frenchman 6-4 6-1, but Djokovic has been relentless this year.
The Serb was again at his dominant best against Japan's Kei Nishikori during his 6-2 6-0 victory.
"I just tried to play the best guy on the tour today, and I was trying to be a little more aggressive and positive, but he was playing too good," Nishikori said of the top seed's form.
"The way he's played today, this week and the last couple of months, it's been amazing, so I'm sure he has a lot of chance (to win the Golden Slam)."
The other semi-final sees sixth-seeded Spaniard Pablo Carreno Busta, who knocked out second seed Daniil Medvedev, facing another Russian in 12th seed Karen Khachanov.
(Reporting by Sudipto Ganguly; Editing by Ken Ferris)