Murray into last four

Andy Murray will play in his first grand slam semi-final after beating Juan Martin Del Potro in an astonishing four-hour epic at the US Open.

The British No.1 looked set for a straight-sets victory but Argentinean teenager Del Potro mounted an inspired fightback before Murray eventually triumphed 7-6 (7-2) 7-6 (7-1) 4-6 7-5 at Flushing Meadows.

Murray, seeded sixth, began superbly but Del Potro has won his last four tournaments and gave everything to try to extend his 23-match winning streak.

Murray wasted little time in winning the first three games of the match but he could not continue in that vein and 17th seed Del Potro fought back to level.

From looking like he would cruise to the first set, Murray suddenly found himself battling to stay in it as double faults and some sloppy errors allowed 19-year-old Del Potro to break again.

The Scot recovered to break back and level at 6-6 and then opened the tie-breaker with an impressive backhand drop shot as he charged the net but mis-hit an attempted repeat from the baseline on the next point.

That was followed by a bizarre exchange as Murray asked officials to turn off the large video screen located high above the seats at Arthur Ashe Stadium.

Officials refused and Murray hit a subsequent forehand wide to fall behind 2-1. But he responded superbly, winning six consecutive points to take a one-set lead as Del Potro threw in some unforced errors.

Despite having his left knee bandaged during the first changeover and receiving treatment throughout the second set, Del Potro had a chance to break serve for a 4-2 lead but could not capitalise.

After both players wasted three break points in the first 10 games of the set, Murray finally went up a break in the 11th game, wasting one opening before taking consecutive points to grab a 6-5 lead when Del Potro hit a forehand into the net.

Murray pumped his fist in celebration, but promptly lost the lead with his worst service game of the match in which he failed to win a point, meaning a second tie-breaker.

However, if Del Potro thought he would have the momentum going into the 13th game he was proved wrong immediately as Murray produced a forehand winner to claim a mini-break.

The Scot then took the next four points to establish a big lead and went on to win the breaker 7-1 to put himself one set away from a first grand slam semi-final.

Del Potro was beginning to look very weary, and it seemed only a matter of time before the Scot wrapped up victory.

That prospect moved a step closer when he broke to go 3-1 up in the third set.

But just like the end of the second set, Murray failed to press home his advantage, allowing the Argentinean to break straight back.

By now Del Potro was playing like he had nothing to lose and suddenly all his big shots were finding their mark.

Murray held to open up a 4-3 advantage but his opponent took the initiative and capitalised on another poor service game from the Briton - who served two more double faults - to lead 5-4.

This time he never looked like faltering while serving for the set and clinched it 6-4 to drag himself back into the match.

Del Potro was by now playing by far his best tennis