Andy Murray could find no way through the formidable defences of Spain's David Ferrer as the home favourite slumped to a 6-4 7-5 defeat in his opening group match at the ATP World Tour Finals on Monday.
Murray broke serve first in both sets but failed to build any momentum as the tenacious Ferrer returned everything the Scot could throw at him.
Ferrer sealed the opening set after 57 minutes when Murray hooked a forehand wide, after which the labouring Murray required treatment on his legs.
Murray went 2-0 ahead in the second set but a dreadful service game gifted back the advantage and Ferrer stuck to his task admirably to clinch victory in exactly two hours.
Later on Monday in the other Group A clash world number one Novak Djokovic begins his campaign against Czech Tomas Berdych.
Rafa Nadal and Roger Federer both won their opening Group B matches on Sunday, although they were pushed to three sets against Mardy Fish and Jo-Wilfried Tsonga respectively.