Former world number one Dinara Safina suffered a shock first-round loss to Kimiko Date Krumm at the Bank of the West Classic in Stanford, United States.
Safina, now down at 35 in the rankings and a wild card here, had served for the match in the second set before crashing to lose 4-6 7-6 (7/0) 6-2 to the 39-year-old Japanese competitor.
Date Krumm will face more Russian opposition in the second round when she meets Elena Dementieva.
Third seed Agnieszka Radwanska was made to work for her place in the second round, as she beat South Africa's Chanelle Scheepers 7-5 4-6 6-3.
Ana Ivanovic showed a welcome and increasingly rare glimpse of form with a 6-3 6-2 win over Alisa Kleybanova.
The win was particularly sweet for Ivanovic as it was Kleybanova who dumped her out of this year's French Open.
There were also wins for Slovakia's Dominika Cibulkova, who saw off Hilary Barte of the United States 6-2, and Olga Govortsova, who had things even easier with a 6-1 win dismissal of Alla Kudryavtseva.