Sloane Stephens, looking to shake off a poor start to the season, notched her biggest victory of 2021 on Wednesday, upsetting eighth-seeded Madison Keys 6-4, 6-4 in the second round of the Volvo Car Open at Charleston, S.C. Stephens lost in the first round of each of her first four events of the year, including the Australian Open, before falling in the second round at the recent Miami Open. On Tuesday, she defeated China’s Xinyu Wang in straight sets before winning an all-United States matchup Wednesday. In two other all-U.S. showdowns, Lauren Davis upset second-seeded Sofia Kenin 4-6, 6-3, 6-4, and Shelby Rogers overtook 13th-seeded Amanda Anisimova 1-6, 7-5, 6-4. American Coco Gauff, the 14th seed, came from behind to beat Russia’s Liudmilla Samsonova 4-6, 6-1, 6-4. Top-seeded Ashleigh Barty of Australian routed Japan’s Misaki Doi 6-2, 6-1, and 12th-seeded Ons Jabeur of Tunisia and 15th-seeded Veronika Kudermetova of Russia also advanced. Fifth-seeded Belinda Bencic of Switzerland and seventh-seeded Elise Mertens of Belgium were eliminated. Copa Colsanitas Switzerland’s Stefanie Voegele needed just 85 minutes to upset top-seeded Saisai Zheng of China 6-4, 6-1 in the second round at Bogota, Colombia. Voegele converted six of her eight break-point opportunities while Zheng managed just two breaks in seven chances. Third-seeded Arantxa Rus of the Netherlands also was upset, falling 7-6 (4), 2-6, 1-6 to Spain’s Nuria Parrizas Diaz. Another Spaniard, Lara Arruabarrena, came from behind to beat sixth-seeded Jasmine Paolini of Italy 2-6, 6-4, 6-2, and Bulgaria’s Viktoriya Tomova dumped eighth-seeded Yafan Wang of China 6-3, 6-3. The day’s other winner was Italy’s Sara Errani.