Andy Murray suffered a collapse in form as a rejuvenated Rafael Nadal won their group match at the ATP World Tour finals in London.
Nadal edged a tight first set and then raced clear in the second to win 6-4 6-1 at the O2 Arena.
He remained on course to reach the semi-finals, after a comprehensive win over the number 2 seed.
Murray plays Wawrinka in his last group match on Friday and can still progress.
The 28-year-old Scot would travel to Belgium next week for Britain’s first Davis Cup final since 1978.