SHANGHAI, China -- Roger Federer has been through a tough stretch -- a sore back, an opening loss at the Masters Cup, a stomach ailment. On Wednesday, he caught a break.
Andy Roddick pulled out of the season-ending tournament hours before their match because of a sprained ankle.
Instead, Federer's opponent was Radek Stepanek, who cut short his vacation in Thailand to compete as an alternate. The 26th-ranked Czech had to borrow rackets from Novak Djokovic because his gear shipped from home didn't clear Chinese customs in time.
The result was a 7-6 (4), 6-4 victory that was far from vintage Federer but kept alive his pursuit of a fifth Masters Cup title.
Simon was added to the field when Rafael Nadal withdrew last week with a knee injury that also forced the 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 a semifinal spot. Djokovic, who is 2-0, has already advanced and will meet Jo-Wilfried Tsonga of France, who has been eliminated after losing his first two matches.
Federer pulled out of the Paris Masters less than two weeks ago because of his back. He still showed some of the rust that was evident in his opening loss to Simon. In particular, his serve was not up to full speed.
The Swiss star said his back was fine but he developed a stomach ailment after the Monday night match against Simon and felt "terrible" when he woke up Tuesday. He spent the day in his room, trying to recover.
"It would have been impossible to play yesterday," he said, looking drained at his postmatch news conference. "Maybe I got lucky that Andy withdrew. And then Radek is not playing with his own rackets, so that made it a little bit more lucky again. I hope with a day of recovery, I'll make a miracle happen here and get through into the semis."
Roddick tried to warm up but said his right ankle, sprained during a warmup drill for practice Tuesday, was severely limiting his movement and his serve.
"Unfortunately that's just not good enough to get it done at a tournament like this," Roddick said, adding the injury did not appear serious. "I didn't feel like I could go out and try to compete and win. It's definitely a tough prospect trying to beat Roger with no serve and not being able to move much.
"The risk-reward wasn't there," he said. "You're risking further injury where it might cut into preparation for next year."
Stepanek won only three points in the first two games but then evened the match. Federer pulled ahead 4-1 in the tiebreak and held on to take the set. Stepanek was broken while serving at 4-3 in the second set. But Federer was broken back at love as he served for the match, netting a forehand after a long rally on break point.
Stepanek pumped his fist and hopped on one leg, but his celebration didn't last long. He missed a backhand volley to set up match point before double-faulting. The loss eliminated him from contention for the semifinals.
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," said Murray, who recently won 14 straight matches.
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 Friday to qualify for the semifinals. He dismissed any suggestion he might take it easy now that he's assured of advancing.
"I don't try and find a balance," Murray said. "I try and beat Federer. Ideally, I'd like to knock him out of the competition if I can. I'd rather not have to play him twice in one week. He's the best player ever."
Murray and Simon were making their debuts at the tournament for the world's top players. Murray jumped ahead 4-0 in the first set and ran off five games in a row in the second.
"I just missed all the opportunities I had today," Simon said. "He didn't miss anything."