Kyle Edmund's good form continued as he reached the second round of the Citi Open in Washington, but fellow Briton Heather Watson lost her opening match.
British number two Edmund, who reached the semi-finals of the Atlanta Open last week, defeated South Korea's Hyeon Chung 6-3 6-1 in 57 minutes.
The 22-year-old will now play number four seed Grigor Dimitrov.
Watson, meanwhile, was beaten 7-6 (7-4) 7-6 (7-3) by Romania's world number 134 Patricia Maria Tig.
The Briton, who squandered set points in the first set, saved two match points before Tig took a second tie-break to win her first match since March.