Washington, DC, USA, 29 July 2014 | tennis.com.au/AAP

Bernard Tomic has continued his solid hardcourt form with a straight-sets victory over Alejandro Gonzalez in the first round of the ATP Citi Open in Washington DC.

Fellow Australian Marinko Matosevic was also victorious, subduing Ukrainian qualifier Illya Marchenko 6-4 7-5.

Tomic dismissed the Colombian 6-2 6-3 in just 57 minutes to advance to a second round meeting with 15th seed Denis Istomin.

The Australian, who won at the ATP Claro Open Colombia in Bogota the week before last, took his winning streak to six matches with Monday’s win over Gonzalez.

He was strong in all areas of his game, landing 10 aces, winning 86 per cent of points on his first serve and hitting 19 winners against just 10 errors in the United States capital.

“I really gave it to him in the first few games which made me feel a little bit more confident out there,” Tomic said.

“Tennis is a lot (about) confidence and I managed to pick up a lot of confidence in Bogota winning my second title.”

Matosevic, who reached last week’s quarterfinals in Atlanta, was pushed by the 170th-ranked Marchenko, requiring more than 90 minutes on court to eventually progress.

The Victorian struggled somewhat on serve, managing just 55 per cent of his first serves and two aces compared with four double faults.

But he played well when it mattered most; from 5-4 down in the second set, the world No.49 reeled off three consecutive games to set up a second round showdown with compatriot Lleyton Hewitt, the tournament’s 14th seed.

Disappointment for Stosur in Stanford

Across the country in California, Sam Stosur fell to a shock 4-6 7-6(7) 7-5 defeat to Japanese qualifier Naomi Osaka at the Bank of the West Classic in Stanford.

Osaka, just 16 years of age and ranked 406th, recorded her first ever WTA main draw win in two hours and 30 minutes.

Osaka saved a match point in the second set and rallied from 3-5 down in the third to progress to the second round, where she will meet either eighth seed Andrea Petkovic or Ajla Tomljanovic.

Stosur has now lost her last four singles matches.