Davis Cup 2015: James Ward stuns John Isner as Great Britain lead United States

James Ward produced a remarkable comeback to stun John Isner and give Great Britain a 2-0 lead after day one of the first round Davis Cup tie against the United States in Glasgow.

Ward was two sets down before shocking the world number 20, who saved five match points, 6-7 5-7 6-3 7-6 15-13 in the longest world group singles match ever after Andy Murray had defeated Donald Young in the opening singles rubber.

Bob and Mike Bryan face a British pair expected to consist of Dominic Inglot and Jamie Murray in Saturday's doubles but after taking the first two singles matches GB stand on the brink of the last eight.

Ward, ranked 111th in the world, who had defeated Sam Querrey in San Diego 13 months ago, took his American opponent to a tiebreak in the opening set but despite taking the lead was eventually outmuscled 7-4 by the big-serving North Carolina-born player.

The second set looked like going a similar way until Isner produced a moment of magic to break the Brit in game 11, leading to a moment of frustration from Ward as he kicked a ball into the crowd, as the USA closed in on levelling the tie.

Those ambitions suffered a blow when Ward produced a break out of nothing after two fine passing shots and halved the deficit with more solid serving as Isner had no answer.

As the match went deep into a fourth set, Isner showed signs of flagging as he started to commit little to the Ward service game, giving the 28-year-old a foothold in the match.

Predictably, the fourth set also went to a tiebreak as Ward successfully served to stay in the match, as the contest threatened to slip into a third hour in Glasgow.

And the match was confirmed to go the distance as Ward dominated the tiebreak 7-3 to take the second rubber into a potentially tie-defining fifth set.

Both players began the set in typically solid fashion but in the eighth game Ward was handed an opening after Isner netted a volley, but he wriggled away with another typically booming serve.

The chances continued to come for Ward however and a match point came his way after a miraculous pass but Isner kept it out with a solid overhead, before a second was snuffed out by another thunderous serve.

With the opportunities gone the pair were now engaged in a slog to the finish, as the physical nature of the contest began to take its tole on both players with Isner suffering with hamstring issues while Ward was being hampered by a hip problem.

Those physical defects allowed Ward to bring up a third match point as Isner went wide with a forehand pass but the whipped chip went agonisingly long from the Brit as the fifth set went to 10-10.

A fourth and fifth match point came and went for Ward as Isner reeled off the errors but the US standard-bearer clung on valiantly but even when his own chances came, via two break point chances in game 23, he was unable to take them.

At the sixth time of asking however, Ward took advantage of the lack of intensity from Isner and at 0-40 up he dumped a volley into the net to send the Emirates Arena into euphoria.