Memphis - Coco Vandeweghe upset South African sixth seed Chanelle Scheepers while British fourth seed Heather Watson battled to advance in opening matches on Sunday at the WTA/ATP US Indoor Championships.
American Vandeweghe defeated Scheepers 6-2, 6-1 while Watson outlasted Kazakhstan's Galina Voskoboeva 7-5, 5-7, 7-6 (7/4) to reach the second round at the $1.58 million hardcourt event.
Watson will next face the winner between American Melanie Oudin and Czech Andrea Hlavackova while Vandeweghe next plays either American Jamie Hampton or Spanish wildcard Garbine Muguruza.
Slovakian seventh seed Magdalena Rybarikova advanced with a 6-3, 6-1 triumph over France's Stephanie Foretz Gacon. Rybarikova will next face American Lauren Davis, who rallied past Kazak Ksenia Pervak 5-7, 6-1, 6-3.
Hungary's Melinda Czink ousted Russia's Olga Puchkova 4-6, 6-3, 6-3 to book a second-round date with either US qualifier Madison Keys or German third seed Sabine Lisicki.
Belgian Kirsten Flipkens is the women's top seed while Croatian Marin Cilic is the men's top seed. Men's main draw matches begin on Monday.