GLASGOW (Reuters) - Juan Martin del Potro delivered a huge blow to Britain's hopes of retaining the Davis Cup when he beat Andy Murray 6-4 5-7 6-7(5) 6-3 6-4 in a five-hour thriller to give Argentina a 1-0 lead in their world group semi-final on Friday.
World number two and Wimbledon champion Murray looked poised to chalk up his 30th victory in 32 Davis Cup matches when he led by two sets to one against the man he beat in last month's Olympic singles final.
But Del Potro, ranked 64th in the world after being plagued by numerous injuries, refused to surrender and condemned Murray to only his third singles defeat in the men's team competition after finishing off the marathon encounter with an ace.
Britain's Kyle Edmund will face Argentina's Guido Pella in Friday's second singles rubber.
The winner will face either France or Croatia in the final.
(Reporting by Pritha Sarkar; Editing by Mark Trevelyan)