SHANGHAI, China — Britain's Andy Murray reached the Masters Cup semifinals with a 6-4, 6-2 victory Wednesday over Gilles Simon of France.

Murray was at his best on the key points, breaking Simon twice in each set and fending off seven of the Frenchman's eight break opportunities.

"It was one of my best matches in recent months," Murray said — quite a statement for a player who recently ran off a 14-match winning streak.

Second-ranked Roger Federer, who lost to Simon in his first match here, was playing later against No. 26 Radek Stepanek, who was added to the field when Andy Roddick withdrew Wednesday after spraining an ankle during practice. Roddick said the injury did not appear to be serious, but that it left him unable to be competitive.

Stepanek, of the Czech Republic, could qualify for the semifinals but would have to win both of his matches and hope that only Murray finishes with two victories in his group.

Murray said he was nervous before the match, knowing that if he lost, he would have to beat Federer in his last round-robin match to qualify for the semifinals.

Both Murray and Simon were making their debuts at the tournament for the world's top eight players, but Murray looked like a veteran, running off the first four games. Simon won only four points in his first two service games.

The Frenchman did get one break back to pull within 4-3, but Murray fended off another break chance on his next serve and easily held to finish off the set.

Simon held to open the second set only to see Murray take the next five games. On match point, the Scot ripped a deep forehand approach shot that Simon couldn't do anything with.

Simon was added to the field when Rafael Nadal withdrew last week with a knee injury that also forced the world's top-ranked player to pull out of next week's Davis Cup final between Spain and Argentina.

In the Gold Group, Nikolay Davydenko of Russia will face Juan Martin Del Potro, with the winner assured of a semifinal spot. Novak Djokovic, who is 2-0, already has advanced and will meet France's Jo-Wilfried Tsonga, who has been eliminated after losing his first two matches.