Defending champion Kim Clijsters withdrew from the Pacific Life Open on Saturday with a left wrist injury.
Clijsters, who is seeded second, injured her wrist during Friday's win against Germany's Angelika Roesch.
Tournament doctors described the injury as a bruised bone on her left wrist and tendonitis.
There were no such dramas for top seed Justine Henin-Hardenne, who won her opening match comfortably, beating Samantha Reeves 6-2 6-2.
Russia's 16th seed Maria Sharapova overcame Flavia Pennetta of Italy 6-3 4-6 6-4.
Jill Craybas - in as a late replacement for Jennifer Capriati - saw her run ended by Spain's Conchita Martinez who won 6-0 6-3.
Henin-Hardenne will play Marta Marrero in the third round after the Spaniard beat Zimbabwe's Cara Black 7-6 6-1.