The opening clash between world number two champion Andy Murray and Argentina's former US Open champion Juan Martin Del Potro was a repeat of last month's Olympic final in Rio de Janeiro.

Murray won a thrilling four hour battle there and it seemed unlikely that this match would hit the same heights.

But it did - and more - as Del Potro's booming forehand took on the tumultuous defence of the reigning Wimbledon winner.

The Argentinian went 2-1 down only to battle back, despite partisan home support, in a match lasting five hours seven minutes.

Del Potro eventually prevailed 6-4, 5-7, 6-7, 6-3, 6-4 for his best win since returning from injury earlier this year.

"I won but I still remember the Olympic final," said Del Potro afterwards.

"This is very important to me and my team and we are looking to reach another final in the Davis Cup.

"Against Andy you never know when the match will finish. 

"He is a dangerous player, a fighter and great champion."

Guido Pella then recovered from a set-down to beat Kyle Edmund in the day's second match.

In what marked a reverse of the opening clash, resolute Argentinian defence proved too much for booming British forehands as Pella prevailed 6-7, 6-4, 6-3, 6-2.

It seems hugely unlikely Britain will now recover from 2-0 down, particuarly because an clearly fatigued Murray is due to play alongside his brother Jamie in the doubles tomorrow.

France are locked at 1-1 with Croatia after day one of the other semi-final at Krešimir Ćosić Hall in Zadar.

Richard Gasquet cruised through 6-2, 7-6, 6-1 again Borna Coric.

Marin Cilic then restored parity, overcoming Lucas Pouille 6-1, 7-6, 2-6, 6-2.

The doubles tie are due to take place tomorrow ahead of two reverse singles on Sunday (September 18).