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 an early lead in their world group semi-final yesterday.

Guido Pella then doubled Argentina’s advantage when he came from behind to beat Kyle Edmund 6-7 6-4 6-3 6-2 and put the Argentines just one win away from reaching their first final since 2011.

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 Rio Olympics 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.

“I won but I still remember the Olympic final. This is very important to me and my team and we are looking to reach another final in the Davis Cup,” Del Potro said.

“Against Andy you never know when the match will finish. He is a dangerous player, a fighter and great champion. In end I played good forehands and good serves and that was key.”

Del Potro capitalised on Murray’s mistakes to take the first set, which included one rally of 41 strokes.

Towards the end of the second, both players were upset by excitable calls of “out” from spectators. That happened on the final point of the set to Del Potro’s fury, the umpire declining to replay it.

He recovered his composure in the third set, taking two of the three successive breaks of serve while running up a 5-3 lead.

But Murray saved a set point with a superb lob and drew level at 5-5 before taking it on the tiebreak.

Del Potro  then showed what he was capable of producing as he pummelled winners from the baseline to bag the next two sets and seal victory.

Other semi-final: Croatia vs France 1-1.