Washington, DC, USA, 22 July 2016 | AAP

The last Australian man left in the Citi Open in Washington DC, Bernard Tomic, has been knocked out in the third round.

Tomic was beaten in straight sets by all-time ATP Tour ace leader Croatian Ivo Karlovic, losing 7-6(4) 6-3.

The Australian had no answer to his 211cm giant’s serve, as Karlovic sent down 21 aces and conceded just 10 points on his own serve.

Tomic was then broken midway through the second set, helping the No.3 seed seal a quarterfinal berth.

Meanwhile Steve Johnson of the United States also won through to the quarterfinals early on Thursday evening (Friday morning AEST).

Johnson accounted for fellow-countryman Ryan Harrison, sweeping through the match 6-4 6-4 in a little over an hour.