A jet-lagged Murray looked sluggish at times during his three-sets win over world No6 Andy Roddick in his opening match in the Red Group on Monday, but the Scot was back to his best as he dispatched world No9 Gilles Simon 6-4, 6-2.

The Scottish world No4, making his first appearance in the showpiece event, still has to play two-time defending champion Roger Federer tomorrow, but will do so certain of a place in the last four and knowing victory will eliminate the former world No1.

"It's great to be in the semi- finals as it's a tough group," said the 21-year-old.

"Roddick is very, very experienced in these competitions. To beat him is never to be underestimated. It's a big win.

"Then Simon obviously is playing the best tennis of his life and he's in the top ten. To beat a couple of top-ten players back-to-back is great.

"The Masters Cup is obviously a huge, huge competition for all the top players and I've got a chance of winning it now."

Murray made a storming start against Simon as he broke twice to take a 4-0 lead, but a string of unforced errors gave his opponent hope and the Frenchman soon started to look like the man who has won three titles this year.

Murray's wobble continued as he missed an overhead smash to hand Simon a break. He then needed to save three break points on his next service game before holding in the tenth to seal the first set.

Murray broke Simon twice at the start of the second set to forge into a lead he never looked like relinquishing as he sealed the win in just over 90 minutes.

"Although he did come back, I was always ahead in the first set," added Murray.

"I was nearly 5-0 up and then he did come back a bit. I got through a tough game at 4-3, once I got through that one I felt pretty comfortable.

"Then, in the second set, I dictated a lot of the points, moved him around a lot and didn't make too many errors. The more I got him moving, the more I changed the pace of the ball and he started to make more mistakes."

While Murray converted four of eight break points, Simon could only manage one from the same amount of opportunities.

"I just missed all the chances I had today," said Simon. "I could have come back to 4-4 in the first, and I missed some easy shots. Then it was the same in the second set.

"But when you play these kind of players it's never easy because he never missed a shot, so you have to play a good point to finish the game."

Elsewhere in the Red Group, Federer kept his tournament alive after beating Radek Stepanek, who was deputising for Roddick who has withdrawn with an ankle injury.

The Swiss posted a 7-6 (7/4), 6-4 win over his Czech opponent, but must triumph in his final Red Group match against Murray to claim a place in the last four.