Elena Rybakina has been bundled out of the first round of the Silicon Valley Classic by Daria Kasatkina in her first game since her Wimbledon triumph last month.

Rybakina won the first set comfortably before the Russian hit back for a remarkable turnaround win, 1-6 6-2 6-0 in one hour and 40 minutes.

Seventh seed Kasatkina was the runner-up at last year's Silicon Valley Classic and found her groove to break her Rybakina six times in the second and third sets.

Rybakina sent down three of her four aces for the match in the first set, but Kasatkina adjusted to her serve and won 52.1 per cent return points for the match.

Eighth seed Karolina Pliskova fought back from a slow start to get past Katie Boulter 1-6 7-6 (7-5) 6-3, despite 16 double faults.

American Amanda Anisimova overcame compatriot Ashlyn Krueger 6-2 7-6 (7-5). US pair Madison Keys and Taylor Townsend were also winners.

Third seed Simona Halep and top seed Jessica Pegula were both among the winners in the first round at the Citi Open in Washington DC.

Two-time major winner Halep cruised past Spanish qualifier Cristina Bucsa 6-3 7-5 in one hour and 20 minutes.

Halep, playing her first match since her Wimbledon semi-final loss to Rybakina, fired 19 winners but also 33 unforced errors.

Defending champion Pegula made light work of countrywoman Hailey Baptiste 6-2 6-2 in 73 minutes.

Pegula will face unseeded Australian Daria Saville, who won in three sets over Mirjam Bjorklund, while sixth seed Kaia Kanepi will meet China's Zhu Lin after both won on Monday.

Fifth seed Elise Mertens was a first-round casualty, going down 7-6 (7-4) 6-4 to Ludmilla Samsonova, while Croatian Donna Vekic knocked off seventh seed Mayar Sherif 6-4 6-1.

Six-time major champion Venus Williams played her first singles match in nearly a year but bowed out 4-6 6-1 6-4 to Rebecca Marino.