A U.S. Open Series eventTuesdayAt The Taube Family Tennis CenterStanford, Calif.Purse: $665,900 (Premier)Surface: Hard-OutdoorSinglesFirst RoundAna Konjuh, Croatia, def. Zheng Saisai, China, 6-3, 6-4. Varvara Lepchenko, United States, def. Mirjana Lucic-Baroni, Croatia, 3-6, 6-2, 7-6 (4). Elina Svitolina (8), Ukraine, def. Kateryna Bondarenko, Ukraine, 4-6, 6-4, 7-5. Ajla Tomljanovic, Croatia, def. Vitalia Diatchenko, Russia, 3-6, 6-0, 6-0. Angelique Kerber (5), Germany, def.