Iga Swiatek said she has not reached her "peak" yet after she ruthlessly moved past lucky loser Eva Lys in 59 minutes to reach the quarter-finals of the Australian Open.

The five-time major winner dropped just one game as she ended Lys' historic run with a 6-0 6-1 victory on Rod Laver Arena.

It is the first time Swiatek, the second seed, has reached the last eight in Melbourne since 2022.

"I'm still 23 years old, so there is a lot to improve always," Swiatek said.

"I don't feel like I'm in my peak yet but matches like that definitely give me confidence. I feel like I'm playing a good game."

Also on Monday, the World Anti-Doping Agency announced it will not appeal against the ban given to Swiatek for a positive test.

She tested positive for heart medication trimetazidine in an out-of-competition sample in August 2024.

The International Tennis Integrity Agency accepted the test result was caused by contamination and Swiatek served a one-month suspension, which ended on 4 December.

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 fourth round of the Australian Open in the Open era.

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.

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.

Earlier on Monday, Madison Keys upset sixth seed Elena Rybakina in three sets to reach the quarter-finals.

The American 19th seed won 6-3 1-6 6-3 on Margaret Court Arena to extend her winning streak to nine matches.

Former Wimbledon champion Rybakina struggled with a back injury in the third round and despite rallying in the second set, was unable to combat 29-year-old Keys' aggressive approach.

"Her serve is such a weapon, so I knew that if I could just try to make at least some of her service games a little bit competitive, then I had a chance," said Keys.

"So I was basically just trying to make anything that I could get my racquet on back over the net, which worked sometimes."

Kazakhstan's Rybakina, 25, said she would need "magic" to progress in Melbourne after needing treatment on her back during her third-round win over Ukraine's Dayana Yastremska.

She had won her previous two matches against Keys, but dropped the first set with the American neutralising her big serve and taking control of the rallies.

Rybakina, a finalist in Melbourne in 2023, fought back midway through the encounter to win four straight games and secure the second set, but Keys would triumph in the decider.

At 3-3 she took control before eventually sealing her spot in the last eight with a searing cross-court winner on her second match point.

Keys will play Ukraine's 28th seed Elina Svitolina in the quarter-finals after she beat Russian Veronika Kudermetova 6-4 6-1.

Svitolina, 30, recovered from a poor start to reach her 12th Grand Slam singles quarter-final, before dedicating the win to her country.

"This fighting spirit that I have is completely Ukrainian spirit that I try to show, that I try to represent, as well," said Svitolina.

"For me to find a way to win matches, to find a way to bring a little light, a little win for Ukrainian people, is something that I feel I am responsible of. To bring the fight is the least that I can do."