Swiatek, who defeated Britain's Emma Raducanu 6-1 6-0 in the third round, conceded just 10 points as she wrapped up the first set in 24 minutes.

She had won 20 straight games across the two matches before Germany's Lys, ranked 128th in the world, eventually managed to hold serve.

"Usually I don't feel comfortable with my game at the Australian Open, but this year it is a bit better," said Swiatek, who will replace Aryna Sabalenka as world number one if the defending champion fails to reach the semi-finals.

Lys was the first women's singles lucky loser to reach the Australian Open fourth round in the Open era and she described her run in Melbourne as "the nicest week in my life".

The 23-year-old had her flight home booked after losing in the final round of qualifying, but she was given a spot in the main draw following Anna Kalinskaya's withdrawal.

"I've had a lot of nights where I was actually talking to my parents, often with tears, asking, 'When will the time come?'," Lys said.

"Because I know I have the potential, but sometimes I was the only person that's really standing in my own way.

"Everything just came down to this week where on one side it's definitely the tennis I played, but also it was the luck in the beginning."

Swiatek will face Emma Navarro in the last eight after the American eighth seed clinched a narrow 6-4 5-7 7-5 win against Russian Daria Kasatkina, the ninth seed.