Ash Barty made quick work of Laura Siegemund on her Stuttgart Open debut with a 6-0 7-5 triumph in just 84 minutes.
The world number one was given a much sterner test by the former champion in the second set but won all 24 points when landing her first serve and had 19 winners to her name.
Next up for the amiable Australian is a meeting with either Jelena Ostapenko or Karolina Pliskova, who made it through to the round of 16 on Wednesday as did Angelique Kerber and Marketa Vondrousova.
Defending champion Petra Kvitova, seeded sixth, had to overcome a second-set blip to earn a 6-3 3-6 6-3 triumph over Maria Sakkari and a spot in the quarter-finals.
Anett Kontaveit continued her love affair with the tournament, upsetting third seed Sofia Kenin 7-5 6-4. She has now reached the quarter-finals or better in each of her four visits to Stuttgart – including a runner-up finish last season.
At the Istanbul Open, seeded pair Daria Kasatkina (4) and Wang Qiang (8) were ousted by Marta Kostyuk and Ana Konjuh respectively in the round of 16.
Katerina Siniakova and Sorana Cirstea both made the quarter-finals, while Kaia Kanepi was a last-32 victor over Zarina Diyas.