Reigning Luxembourg Open champion Misaki Doi suffered a first-round loss against America's Lauren Davis on Tuesday.
The Japanese put up a meek defence of her title as the sixth seed fell to a 6-1 6-2 loss in little over an hour.
Her unhappy experience was in stark contrast to the other seeds in action, as Petra Kvitova, Caroline Wozniacki, Kiki Bertens and Johanna Larsson won in straight sets.
In-form Wozniacki, who has won events in Tokyo and Hong Kong in the past month, beat Madison Brengle 6-2 6-2.
She is seeded second behind Kvitova, who stepped up a gear in the second set to defeat Hsieh Su-wei 7-5 6-0.
In other matches, 2015 beaten finalist Mona Barthel overcame Carina Witthoft 6-1 6-4, and there were wins for Kristyna Pliskova, Tereza Smitkova, Andrea Petkovic and Sabine Lisicki.