Briton Murray appeared to struggle physically in the third and fourth sets of the match.

"I don't know why I felt the way I did," Murray said. "I haven't felt like that in a very, very long time, since I was maybe 20 or 21. I think the last two, three years it's not the reason why I've been losing matches. I can't explain it."

Murray became frustrated as the match wore on, repeatedly berating himself and looking to his camp for support. Wawrinka capitalised on the demeanour and condition of his opponent and pushed out a 6-7 7-6 6-3 6-3 win in just under four hours.

The Swiss goes on to face American Sam Querrey for a place in the quarter-finals.

Murray meanwhile will look to his camp to find a solution and reason for his shock defeat.