The Scot, who was third seed, was beaten 6-4, 6-3, 6-2 in the quarter-final as ninth-seeded Wawrinka proved his form at Flushing Meadows, New York.
In his post-match press conference, Murray said: "I don't think I was playing poorly. I got to the quarter-finals of a slam, which isn't easy. I would have liked to have played a little bit better but I've had a good run the last couple of years. It's a shame I had to play a bad match today."