A SENSATIONAL performance from James Ward has left Great Britain on the verge of victory over the USA after a dramatic day in the Davis Cup in Glasgow.

It also prompted Andy Murray, his stunned team mate, to tweet: "Time to remove every item of clothing and run through the streets of Glasgow. Absolute farce from @JamesWardtennis."

Ward, ranked 111th in the world, defeated John Isner, ranked 20th, after losing the first two sets. His marathon win in the Emirates Stadium gave Britain a 2-0 lead after Andy Murray, the world No.5, had dismissed Donald Young in four sets.

Great Britain now need only one victory from today's doubles or the reverse singles tomorrow to progress in the world group.

Murray was the homecoming hero defeating Young 6-1, 6-1, 4-6, 6-2 in front of 7700 roaring fans on his first playing appearance in Scotland since winning Wimbledon but it was Ward who proved the unlikely star of a wonderful day for Team GB.

The 28-year-old Londoner was the toast of Glasgow after he battled back to slaw the 6ft10ins giant of Isner 6-7 (4), 5-7, 6-3, 7-6 (3), 15-13 in a match that stretched to four hours and 57 minutes, threatening at one point to replicate the American's struggle with Nicolas Mahut at Wimbledon in 2010 that was an elongated 11 hours and five minutes.

Mercifully, Ward, who regularly punches above his weight in the Davis Cup with a 10-7 record, finally knocked out Isner on the sixth match point to the roaring delight of a home crowd.

Ward described the atmosphere during his titanic struggle as the best he had ever experienced, with Leon Smith stating simply that the crowd had vindicated the decision to bring the tie to Glasgow.

He said Ward's performance was ''phenomenal" with his player beating a player who regularly in the top 10 of the rankings.

Ward was supported at every change of ends with Murray particularly voluble.

The Englishman said: "To have Andy there living every point is something I have never experienced before and it is a special moment. He is probably my best friend in tennis. I train with him in Miami and he knows how hard I work. Likewise, I know how hard he works so it was good to share the moment together.''

He said those training blocks in Miami contributed significantly to outlasting Isner over five hours.

Isner limped into the press room with an ice pack on his knee, declaring that his hurt was more mental than physical: "I have lost a lot of tough matches before. They suck. It's brutal. I am not going to sleep tonight. It's awful. Mentally, I am a bit shaken right now."

He praised Ward, saying: "He played pretty well, he stayed composed. Credit to him."

The USA must win today's doubles match to keep the tie alive. Mike and Bob Bryan, the best pair in the world, will almost certainly now take on Jamie Murray and Dominic Inglot. Andy Murray is almost certain to be kept back for the match against Isner that would win the tie if the Bryans, the world's bests pairing, put a point on the board for USA.

Smith would offer no hint of his thinking last night, saying he would have a conference with his players before deciding on the pairing.

Jim Courier, the USA captain conceded: "History is not kind to teams who go down two-zero." But he said all hope was not lost, particularly if the Bryan brothers turned the tide today. He said Isner could beat any player in the world and he had faith in Young defeating the hero of the day in Ward.

Earlier, Murray came on to an uproarious reception from the capacity crowd to dismiss Young who was overwhelmed by the Scot from the beginning.

"He didn't start the match well. He didn't have a good first game, but I made one unforced error in the first two sets," he said.

"I can't say it was down to his bad play why I was in that position. I'm going to praise myself today, I had one unforced error in two sets. That's going to get you in a 6-1, 6-1 lead in these sort of matches."

Murray accepted the crowd was loud and supportive but added: "If he was intimidated then I also think I played my part as well."

Young will now play Ward, the hero of an extraordinary day in the East End of Glasgow. The American said of Murray: "I think he just played great to be honest. You cannot really prepare for the atmosphere which was awesome, even though the crowd was 98% for him."

He pointed out that Murray's unerring play had made him impossible to counter. Young, ranked 47th in the world, took some comfort from winning the third set after losing the first two in 45 minutes.

He said of the minor resurgence: "He started to miss a little more, I kinda loosened up. I was getting whupped pretty good so I started to hit the ball and was able to string some points together in a row and get into his service games which I could not do in the first two sets."

USA now need to stage the sort of fightback staged by Ward last night. The odds are gainst this, but they were against the Englishman too.