World setter Novak Djokovic needed an hour and 14 minutes to beat German Jan-Lennard Struff in the round of 16.
The Serb won in two straight sets at Ariake Tennis Park - 6-4, 6-3.
In the eighth round of the Olympics, Djokovic will face sixteenth-seeded Spaniard Alejandro Davidovich Fokina.
Novak Djokovic can this year repeat the feat that only Steffi Graf has succeeded in - taking home a Golden Slam.
That is, during the same year, win all four grand slam tournaments and become Olympic champion.
In 2021, the 34-year-old has won the Australian Open, French Open and Wimbledon.
And is top-seeded in the Olympics where both Rafael Nadal and Roger Federer do not participate.
The fourth grand slam tournament, the US Open, is decided after the Olympics.
MORE FROM TOKYO: Here the boat stops the start of the men's triathlon (July 26, 2021)
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Chaotic start of the men's triathlon - which the Norwegian Blummenfelt won Photo: Discovery +