Qualifier Aslan Karatsev stunned eighth seed Diego Schwartzman to reach the Australian Open fourth round, but Alexander Zverev made light work of Adrian Mannarino on the fifth day.

World number 114 Karatsev, making his first Grand Slam main-draw appearance, beat the Argentine 6-3 6-3 6-3.

The Russian has not dropped a set since the first round of qualifying.

Sixth seed Zverev, a semi-finalist at Melbourne Park in 2020, beat France's 36th-ranked Mannarino 6-3 6-3 6-1.

Karatsev will play one of Canadian duo Denis Shapovalov or Felix Auger-Aliassime next.

He has mostly played on Challenger events - the level below the ATP Tour - and has previously lost in qualifying for every major.

Zverev, who lost the US Open final to Dominic Thiem in September, dropped his opening set of the tournament against American Marcos Giron.

He has not lost a set since and he did not look troubled against Mannarino, saving all four break points he faced and hitting 35 winners to his opponent's 11.

It is just the second time in 27 attempts that the German has beaten a top-50 player in straight sets at a Grand Slam.

He will play either Pedro Martinez of Spain or Serbia's Dusan Lajovic for a place in the quarter-finals.

He is joined in the fourth round by Bulgarian 18th seed Grigor Dimitrov, who advanced when opponent Pablo Carreno-Busta retired with an injury.

Dimitrov led 6-0 6-1 when the Spaniard withdrew after taking a medical timeout for abdominal treatment.

Defending champion Novak Djokovic is in action later on the fifth day, taking on American 27th seed Taylor Fritz.

Home favourite Nick Kyrgios also continues his bid against third seed Thiem hours before Melbourne enters a five-day lockdown because of a coronavirus outbreak.