Former US Open champion Sloane Stephens and Slam finalist Madison Keys lead a strong USA contingent in the 32-strong singles field for next month's Citi Open.

They are joined by a trio of compatriots - Hobart champion Sofia Kenin, Jennifer Brady, and Jessica Pegula - with nine entrants to follow.

Keys returns to the tournament for the first time since 2014; Stephens was the 2015 champion at the Citi Open, beating Anastasia Pavlyuchenkova in the final 6-1, 6-2 - and the Russian will also join the field.

Another Top 20 star, Switzerland's Belinda Bencic, will also be in Washington DC, aiming to extend her sensational season so far, with 30 match wins under her belt.

Stephens and Keys are not the only competitors to have featured in a Slam final; the field also includes two-time Slam runner-up and former World No.2 Vera Zvonareva, and Wimbledon finalist Eugenie Bouchard.

Sofia Kenin with the Hobart trophy (Getty)

Canada's Bianca Andreescu hopes to have returned from injury by then so she can resume what was proving to be a stunning season, winning her first Premier Mandatory title at Indian Wells.

READ: Bianca Andreescu - 'My goal was to make history - and I just did'

Italy's Camila Giorgi, last year's Wimbledon quarterfinalist, is also in the main draw, as is Katerina Siniakova, who was one-half of the winning pairs in last year's women's doubles and mixed doubles at the All-England Club.

Other entrants include Hsieh Su-Wei, Lesia Tsurenko, Kristina Mladenovic, Barbora Strycova, and Olympic gold medalist Monica Puig.

Tickets for the Citi Open are available now through and can be bought for a single session or in packages.