4 September 2013 Last updated at 10:01

Andy Murray at US Open 2013: Briton looking for consistency

US OPEN

  • Venue: Flushing Meadows, New York
  • Date: 26 August - 9 September

Coverage: Commentary on BBC Radio 5 live sports extra, via the BBC iPlayer Radio app, BBC Sport website & BBC Sport app; updates on BBC Radio 5 live; live text commentary on BBC Sport website, app & mobile devices

Defending champion Andy Murray admits he struggled with the conditions after beating Uzbekistan's Denis Istomin in four sets to reach the quarter-finals of the US Open.

The Briton was irritated by a number of bad line calls and battled for consistency on a windy evening, but was not seriously threatened in a 6-7 (5-7) 6-1 6-4 6-4 win.

Murray will next face Stanislas Wawrinka in the quarter-finals on Thursday and says he expects a tough test against a steadily improving player.