Andy Murray has hinted that he is struggling to motivate himself following his historic Wimbledon victory.
The Scot became the first British player since Fred Perry to win the title at SW19 when he beat Novak Djokovic in straight sets, ending a 77-year run without a home winner.
Since returning to the court, the 26-year-old Glaswegian has suffered early exits in the Rogers Cup and Cincinnati Masters, but he maintains that 2013 has been a resounding success story.
"When you work hard for something for a lot of years, it's going to take a bit of time to really fire yourself up and get yourself training [at] 110%," Murray told reporters.
"I have played my best tennis in the slams the last two, three years. I lost today in straight sets, so that's disappointing.
"I would have liked to have gone further, but I can't complain. If someone told me before the US Open last year I would have been here as defending champion having won Wimbledon and Olympic gold, I would have taken that 100%."
Wawrinka will play the winner of Novak Djokovic and Mikhail Youzhny for a place in the final in New York.
