Washington, DC, USA, 2 August 2017 | AAP

Australian Jordan Thompson is into the second round of the Citi Open in Washington DC after a straight-sets victory over Belgian Ruben Bemelmans.

World No.75 Thompson won 6-3 6-2 in the first round of the ATP event in the US capital on Tuesday, setting up a clash with young gun Alexander Zverev.

He was dominant on serve against Bemelmans, breaking his world No.98 opponent five times in the match and winning 80 per cent of points on first serve to 61.

He claimed victory in just over 80 minutes, good signs ahead of Australia’s Davis Cup semifinal against Belgium in September.

Thompson faces a tough task against world No.8 Zverev as he aims to improve on his second-round exit in Washington last year.

In other results, American Jack Sock reached the third round with a 7-6(2) 7-6(6) victory over Marius Copil.

Kyle Edmond, Dmitry Tursunov and Marcos Baghdatis were also first-round winners.