Germany's Alexander Zverev won his fourth ATP title of the season with victory over South African Kevin Anderson in the final of the Citi Open.
The 20-year-old world number eight won 6-4 6-4 in 69 minutes in Washington.
Zverev is the youngest player to win four titles in a season since Juan Martin del Potro in 2008.
Russia's Ekaterina Makarova beat Germany's Julia Goerges 3-6 7-6 (7-2) 6-0 in the women's final to secure her third WTA singles title.
Elsewhere, Madison Keys beat fellow American Coco Vandeweghe 7-6 (7-4) 6-4 to win the Stanford Bank of the West Classic in California.
The US Open, the fourth and final Grand Slam of the year, begins on Monday, 28 August.