Top seeds Petra Kvitova, Caroline Wozniacki and Kiki Bertens advanced to the second round of the Luxembourg Open.
Kvitova, the Czech No.11, progressed with a 7-5 6-0 win over Su-Wei Hsieh of Chinese Taipei.
Dane Wozniacki beat Madison Brengle 6-2 6-2, while Bertens saw off Annika Beck of Germany 6-4 6-4.
Sixth seed Misaki Doi, though, is out after the Japan player was defeated 6-1 6-2 by Lauren Davis.
Johanna Larsson, the Swedish eighth seed, beat Pauline Parmentier 6-4 6-2, while Kristyna Pliskova is also through after she came from behind 3-6 6-3 6-4 against Oceane Dodin.
In Tuesday's late match, Sabine Lisicki, the German who reached the 2013 Wimbledon final, came through in three sets against Viktorija Golubic 6-3 3-6 6-2.