Andy Murray teased and tormented Juan Martin Del Potro into submission to reach his first Grand Slam semi-final. But he will need to add world-class power to clever strategy if he is to overcome world No1 Rafael Nadal.

Murray defeated 17th seed Del Potro 7-6, 7-6, 4-6, 7-5 after three hours and 58 minutes of tense combat here, with the 19-year-old Argentinian reduced to tears of frustration in his post-match interview.

But Murray will now have to raise his game, which featured numerous floated sliced backhands, when he takes on Nadal. The Spaniard started slowly against Mardy Fish and it was well past midnight by the time he saw off the American 3-6, 6-1, 6-4, 6-2. By then, however, he was back to his brutal best.

Without a win in their five previous meetings. including a straight-sets defeat in this year's Wimbledon quarter-finals, Murray is still upbeat about taking on Nadal.

He said: "The one thing that I need to improve is to return better. If I take the Wimbledon match away, then in the times I have played him on hard courts, there have been a few close sets and really tough matches.

"It comes down to who returns better and who gets the breaks of serve.

"Normally that's the best part of my game. How you do in Slams is how you're remembered in tennis, and I wanted to improve my record in them this year."

Murray, 21, has become only the third British player to reach the US Open men's semi-finals in the open era, joining Greg Rusedski (1997) and Tim Henman (2004). Only Rusedski made it into the final, where he lost to Pat Rafter.

The British No1 is not a fan of the Super Saturday concept - made for television - which means the men's semi-finals take place just 24 hours before the final.

Normally, there would be a day's rest for the players and Murray said: "I think it's better if they play Friday then Sunday. The players should be able to give it their best shot because it's a Slam final. If a guy plays a 7-6 in the fifth set in a match lasting over four-and-a-half hours and the other guy plays for 90 minutes, I know who I'd be putting my money on the next day."

But his match against Del Potro finally ended the bitterness that followed their meeting in Rome earlier this year which saw the Argentinian aim a ball at him and complain about Judy Murray shouting encouragement at her son.

Murray who led by two sets and 3-1 before allowing Del Potro back into the contest, said: "Quite early on in the match there was sort of a feeling of respect between us. There was no arguing over line calls or anyone trying to get in anyone's face. I think a lot was made of what happened the last time I played against him. I said it wasn't going to be a problem and at the end of the match he said, 'I'm sorry for what happened before.' It's all in the past."

With the match lasting just short of four hours it became the first day-night contest of this year's Open and caused huge problems for the organisers and host broadcaster. The crowd watching Murray's triumph had to be quickly cleared out of the biggest stadium in world tennis to bring in the next full house to witness the Williams sisters and then the Nadal-Fish contest.

It was a chaotic end to a milestone day in Murray's tennis life. The Briton showed that he is now starting to use big-match experience to his own advantage.

The fans booed Murray when he kept asking for the video challenge system to determine close line calls. He knew there was little chance of getting the verdict but the aim was to break up Del Potro's rhythm on serve and to buy himself time. And it worked.

Del Potro came into the match with four successive titles and 23 wins in a row but was stretched to his physical and emotional limit. After the post-match questions turned to his native Spanish, he had to be helped away after breaking down in tears. This is what Murray is now capable of achieving; the mental and physical demolition of highly-rated players.

Del Potro was magnanimous in defeat and said: "I was feeling pain in all my body, but I just did my best. We played a good match. Andy produced a very good performance and is in good shape. Today, I played against one of the best players of the world."

Murray will practise later today and then watch his older brother Jamie partner American Liezel Huber in the mixed doubles final against Leander Paes and Cara Black.

Meanwhile, British juniors Marcus Willis and Dan Smethurst lost their second-round matches, leaving Dan Cox as the only survivor.