Top seeds Barbora Zahlavova Strycova and Sofia Arvidsson both lost opening-round matches in straight sets at the Cellular South Cup on Monday.
No. 1-seeded Zahlavova Strycova, of the Czech Republic, lost 6-1, 6-3 to Michaella Krajicek of the Netherlands.
No. 2 Arvidsson, a Swede who won her first title at the 2006 Cellular Cup, lost 6-3, 6-1 to American Alexandra Stevenson. Arvidsson was a finalist last year, losing to champion Maria Sharapova, who did not return this year to defend her title.
American Melanie Oudin, seeded No. 3 in the women's bracket, defeated Anastasia Pivovarova of Russia 6-4, 6-0, while sixth-seeded Rebecca Marino of Canada downed American Jamie Hampton 6-4, 6-1.
Oudin next will play Evgeniya Rodina of Russia, who rallied to beat Croatia's Ajla Tomljanovic 1-6, 6-0, 7-6 (5).
In addition to the top two seeds departing, fifth-seeded Olga Govortsova of Belarus dropped a three-set match to qualifier Stephanie Foretz Gacon of France, 6-3, 4-6, 6-4.
On the men's side, eighth-seed Kevin Anderson of South Africa lost to American Robert Kendrick 5-7, 6-3, 7-6 (4).
Anderson was the only seeded player in Monday's opening round of the men's draw.
Top-seeded Andy Roddick and fifth-seeded Sam Querrey of the United States open play Tuesday, while Canada's Milos Raonic and second-seeded Fernando Verdasco of Spain play Wednesday in a rematch of Sunday's final at the SAP Open.
Raonic defeated Verdasco, the ninth-ranked player in the world, 7-6 (6), 7-6 (5) for his first title.
