|2020 US Open|
|Venue: Flushing Meadows, New York Dates: 31 Aug-13 Sept|
|Coverage: Selected live radio and text commentaries on BBC Radio 5 Live Sports Extra, BBC Sounds, the BBC Sport website and app.|
Two-time Grand Slam champion Garbine Muguruza has been knocked out of the US Open, losing in straight sets to Tsvetana Pironkova.
The Spanish 10th seed, who reached this year's Australian Open final, lost 7-5 6-3 at Flushing Meadows.
Pironkova, 32, is playing her first tournament since Wimbledon 2017, after which she gave birth to her first child.
"I didn't expect my first tournament to be so good," said Pironkova.
"It's welcome. That's why I came back, for these matches and these stages."
The Bulgarian will play Croat 18th seed Donna Vekic next in New York.
Elsewhere, former world number one Victoria Azarenka continued her fine form by beating fellow Belarusian and fifth seed Aryna Sabalenka 6-1 6-3.
Azarenka won her first WTA Tour title since 2016 at last week's Western and Southern Open.
Australian Open champion Sofia Kenin beat Canada's Leylah Fernandez 6-4 6-3.
The 21-year-old American, seeded second, will face Tunisian 27th seed Ons Jabeur in the third round.
American 2017 champion Sloane Stephens - seeded 26th this year - cruised through to round three with a 6-2 6-2 win over Olga Govortsova of Belarus.
The 27-year-old will next play 23-time Grand Slam champion Serena Williams, who saw off Margarita Gasparyan 6-2 6-4.
Seventh seed Madison Keys, who Stephens defeated in the final three years ago, will play France's Alize Cornet after defeating Spain's Aliona Bolsova 6-2 6-1.
Amanda Anisimova, 19, came from behind to see off 16-year-old fellow American Katrina Scott 4-6 6-4 6-1.