France's Amelie Mauresmo became the first big-name casualty at the Stuttgart Grand Prix by losing 6-2, 7-5 to Russian Elena Dementieva.
Amelie Mauresmo is 12th in the WTA rankings
Mauresmo, ranked 12th in the world, said: "I just didn't play well in the first set and playing someone like Elena you need rhythm from the start."
Meanwhile Serena Williams opened her campaign with an easy 6-0, 6-0 win over the Czech Republic's Zuzana Ondraskova.
And defending champion Nadia Petrova also progressed to the second round.
The seventh-seeded Russian will play Italian Karin Knapp in the second round and looks set for a show-down with third seed Jelena Jankovic in the third round.
Earlier in the day, Poland's Agnieszka Radwanska beat France's Wimbledon finalist Marion Bartoli 0-6, 6-2, 6-1.