Novak Djokovic resumed his quest for a “Golden Slam” and the Olympic gold medal Saturday, easily dispatching Hugo Dellien of Bolivia in straight sets.

But tougher challenges await Djokovic, the world No. 1, and he got an early feel for what might serve as his biggest foe — the sweltering Tokyo summer.

When tennis players talk about how the Olympic tennis competition feels different than any other tournament, they are usually referring to representing their country — playing for national pride and a medal rather than simply prize money or points in the professional standings.

This year, there is that, but this is also shaping up to be one of the hottest and most uncomfortable tennis tournaments they will ever play in their lives. As play got underway Saturday morning temperatures were approaching 90 degrees in the shade. The combination of the sun, the humidity and the hardcourts made it feel far hotter than that on the courts.

Temperatures can be higher in Australia occasionally, but it is usually a dry heat. Cincinnati in August and the U.S. Open in late summer in New York have their oven-like days as well, but those days are shorter, and there are evening and night matches, too.

With the sun high throughout the afternoon there was little shade anywhere on any of the courts. There is a reason tennis tournaments in this part of the world take place in the fall.