Iga Swiatek continued her impressive form as she crushed qualifier Eva Lys at the Stuttgart Open to clinch a 20th successive win and sail into the quarter-finals.

The world number one was far too good for her opponent, as she claimed her 6-1 6-1 victory in slightly over an hour.

Swiatek, 20, last lost a match in February and has not dropped a set since Indian Wells in March, winning each of the last 26 – that is the best such run on the WTA Tour since Serena Williams won 28 successive sets between the 2012 US Open and 2013 Australian Open.

Having won each of the past three events she has entered, Swiatek is the hot favourite to make it four on the bounce in Stuttgart, where she could meet reigning US Open champion Emma Raducanu next in the last eight.

Raducanu, seeded eighth, began her campaign with an emphatic 6-1 6-2 win over Australia's Storm Sanders on Wednesday to set up a second-round clash with Tamara Korpatsch – the winner faces Swiatek.

Sixth seed Karolina Pliskova overcame compatriot Petra Kvitova 6-4 4-6 7-6 (7-5) to progress, while Anett Kontaveit – the fifth favourite – saw off Angelique Kerber 3-6 6-4 6-4.

It was a bad day for some of the higher seeds in the Istanbul Cup, as three of the top five were eliminated.

Favourite Elise Mertens retired from her tournament opener with Rebecca Peterson due to a leg injury, though the Belgian was already 7-5 4-1 down.

Anhelina Kalinina and Jil Teichmann – seeded fourth and fifth, respectively – suffered surprise defeats as well.

Defending champion and second seed Sorana Cirstea appeared in danger of following them out as well, but rallied to defeat Arantxa Rus 3-6 6-1 7-5.

Ajla Tomljanovic also progressed, the Australian enjoying an impressive start against her countrywoman Jaimee Fourlis, winning 6-1 6-3.