Fourteen-time Grand Slam winner and top seed Djokovic is gunning for a record seventh Australian title.

He dropped a set for the first time this year against fast-rising Canadian Denis Shapovalov, before demolishing him in the fourth stanza to win 6-3, 6-4, 4-6, 6-0.

"I just tried to be in the moment and weather the storm," said the Serb, who was unsettled when the lights were switched on in Rod Laver Arena for television reasons, despite it still being daylight.

"Completely unnecessary to turn on the lights," he said in roasting the organisers.

Djokovic's victory means he is guaranteed to stay world number one when the new rankings are released after the tournament.

He next plays another up-and-coming star, Russia's 15th seed Daniil Medvedev, who eased past David Goffin and has yet to drop a set.

Another young gun Alexander Zverev made the last 16 for the first time when he swatted aside Australian Alex Bolt with a comprehensive 6-3, 6-3, 6-2 win in three sets and will play former world number three Milos Raonic for a place in the quarter-finals.

The 21-year-old German number four seed and flagbearer for the next generation of young players cruised into the last 16 of the Australian Open for the first time in just 112 minutes.

But the world number 155 was never allowed a chance against the man who won the ATP Tour Finals, beating Roger Federer and Novak Djokovic on consecutive days in the process.

Eighth seed Kei Nishikori made it back-to-back victories for Japan, following Osaka on court by beating Portugal's 44th-ranked Joao Sousa in three sets.

The 29-year-old has won all three of his first week matches on Margaret Court Arena to reach the last 16 for the seventh time in nine appearances.

"I love to play this court," said the 2014 US Open finalist after delighting a large contingent of Japanese fans.

He next plays Spain's 23rd seed Pablo Carreno Busta.