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.
The Spaniard could qualify for the semi-finals on Wednesday, depending on the result of the evening match between Stan Wawrinka and David Ferrer.
Murray plays Wawrinka in his last group match on Friday and can still progress.
The 28-year-old Scot will travel to Belgium next week for Britain's first Davis Cup final since 1978.