The British number one, inset, and sixth seed reached the last four of the US Open in New York last night with another thrilling victory at the Billie Jean King National Tennis Centre, holding off the 17th seed Juan Martin Del Potro in a four-hour, four-set battle having led by two sets and a break against the Argentinian teenager.

It is the furthest 21-year-old Murray has progressed in any of the four grand slams having made it to his first quarter-final in a slam at Wimbledon earlier this summer. Yet with the semi-finals set for Saturday, the Scot said he would leave his pre-match planning until the last possible minute.

"I won't think about it much," Murray said following his 7-6 (7-2) 7-6 (7-1) 4-6 7-5 victory over Del Potro.

"I'm sure the night before the match I'll think about it a bit, and then the day off I'll obviously speak to my coach and talk about the game plan and stuff."

Murray will play Rafael Nadal in the semi-finals after the world number one defeated American Mardy Fish 3-6 6-1 6-4 6-2.

The other two men's quarter-finals take place today with Gilles Muller taking on Roger Federer and Andy Roddick facing Novak Djokovic.