Andy Murray claimed a place in the semi-finals of the Masters Cup with a 6-4, 6-2 victory over tenacious Frenchman Gilles Simon on Wednesday.

The 21-year-old world number four fended off a mid-match fight-back from Simon to join Serb Novak Djokovic [Images] in the last four on his debut at the $4.45 million (2.90 million pound) season finale.

"It's great," said Murray, who beat American Andy Roddick [Images] in his opener. "To beat a couple of top-10 players back-to-back is great. The Masters Cup is obviously a huge, huge competition for all the top players. I've got a chance of winning it now."

Roger Federer [Images] kept his hopes of a fifth Masters Cup title alive with an unconvincing 7-6, 6-4 victory over Radek Stepanek, the world number 27 who replaced Andy Roddick when the American pulled out with an ankle injury earlier in the day.

Defending champion Federer, who said he had been laid low with a stomach upset after losing his opening match to Simon on Monday, started with a break in the first service game but looked well below his best and allowed the Czech back into the match.

The world number two needed a tiebreak to win the first set and was broken when serving for the second, finally clinching his first win of the week when Stepanek double faulted.

The 27-year-old must beat Murray in his final group match on Friday to avoid going out of the season-ender at the group stage for the first time.

"At the end of the day I still have a chance," said the Swiss. "I hope with a day of recovery, I'll make a miracle happen here and get through into the semis."

Simon, who won his place at the event when injured world number one Rafael Nadal [Images] pulled out, could still qualify from the group at Federer's expense despite losing to Murray.

The French world number nine again impressed but paid the price of converting just one of eight break points he held on Murray's serve.

"It's difficult when you play this kind of player because he never misses a shot so to beat him you have to make a good shot every time and I didn't," he said.

Murray also beat the 23-year-old in the Madrid Masters final last month and started confidently, grabbing two breaks after some long opening exchanges to lead 4-0.

Simon, though, showed in his victory against Federer that he could be an awkward customer and he slowed his game down to shift the balance of the match.

Breaking back for 4-2, he had two break points on Murray's next service game but fluffed his first chance before the Scot muscled up an ace to save the second and go 5-3 up.

"Every time you play against a good player they're going to come back, they're going to start raising their level," said Murray, who served out to go a set up two games later.

"He's confident just now. It's not like I was playing bad tennis."

The Frenchman had more break points in Murray's first service game of the second set but once those were gone, so was Simon's chance.

"The more I got him moving, the more I changed the pace of the ball, he started to make more mistakes," said Murray, who wrapped up the match after 93 minutes when Simon netted.

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