Djokovic eased to a 6-2 6-2 victory over Bolivia's Hugo Dellien but tougher assignments lie between him and a much-coveted gold medal for Serbia, and the weather could yet prove his most difficult opponent.

It is well known that the world No.1 struggles with heat and humidity, and he said with a wry smile: "I'm still waiting to meet the player that likes this kind of weather.

"Playing in extreme heat and humidity that is 90 per cent or God knows how much, it's very challenging.

"Obviously it's the same for everyone and it's something we've known coming into Tokyo, we expected that the conditions were going to be very tough, but before you come here and experience that you don't really know how difficult it is."

Matches played at ATP and WTA tournaments held in similar conditions often do not start until late afternoon but here all courts start at 11am, meaning players are competing in the hottest part of the day.

Later starts were considered but, with organisers the International Tennis Federation having to plan for potential rain or extreme heat breaks, as well as a lack of infrastructure for late finishes, a daytime schedule was deemed best.

Djokovic said: "I don't really get why ITF doesn't want to move the matches. This was the last centre court match and it was finished before 5pm."

Djokovic, who is bidding to become the first man to win a golden slam of all four major titles and singles gold in the same year, will next take on German Jan-Lennard Struff, while second seed Daniil Medvedev also found the conditions tough in a 6-4 7-6 (10-8) victory over Alexander Bublik.

Australian Associated Press