WASHINGTON -- Top-seeded Sloane Stephens was upset in the first round of the Citi Open on Tuesday, and Coco Gauff also lost in the tune-up for the US Open.
Rebecca Peterson beat Stephens 6-2, 7-5 at the hard-court tournament. Stephens was coming off a third-round loss at Wimbledon.
Gauff, the 15-year-old who reached the fourth round at Wimbledon and got into the Citi Open as a qualifier, lost 6-4, 6-2 to Zarina Diyas.
Stephens is ranked eighth, and Peterson is 70th. Stephens won the Citi Open in 2015 and reached the 2017 doubles final. Peterson, from Sweden, will face Italian Camila Giorgi in the second round. Giorgi posted a 6-2, 7-5 win over Sachia Vickery of the United States.