Federer shines as Djokovic survives heat test

But with temperatures touching an energy-sapping 40 Celsius and ice-towels in use, 2014 winner Stan Wawrinka both wilted and were knocked out.

World number one Simona Halep was also convincing in her straight demolition of Canadian Eugenie Bouchard.

Swiss 19-time Grand Slam champion Federer disposed of Jan-Lennard Struff 6-4 6-4 7-6 (7/4), avoiding the worse of the furnace-like conditions in his night match.

"I practice with him so I had the information I needed," he said, adding that the heat doesn't bother him. If you want to get to the top, you've got to play in all conditions." It was never going to be easy for the German. While Federer had made at least the third round each year since his Melbourne Park debut in 2000, Struff had failed to go further than the second round at any Grand Slam.

Six-time Melbourne champion Djokovic had a much tougher time, coming through a four-setter against Gael Monfils in a thorough examination after being out for six months with an elbow injury.

He lost the first set before Monfils began struggling in the second and was heard at one point telling the umpire: "I'm tired and dizzy."

The Frenchman remarkably recovered to make a fight of it before a relieved Djokovic, seeded 14, came through 4-6 6-3 6-1 6-3.

"It was tough conditions, brutal, especially the first 90 minutes," he said. "I'm still not 100 per cent, but building. I have a lot of faith and self-belief."

Wawrinka failed to progress, clearly still struggling from a lengthy knee injury lay-off in his straight sets defeat by Tennys Sandgren.