SHANGHAI, China - It wasn’t hard for Roger Federer to find a silver lining in his Masters Cup loss.

The aching back that forced him to withdraw from the Paris Masters 10 days ago was fine, and he still has a shot to win the season-ending event for the top eight players on the men’s tennis tour.

“I’m definitely in a more positive mind-set today just because my back feels good,” the second-ranked Federer said after losing to Gilles Simon of France 4-6, 6-4, 6-3 Monday.

In the other Red Group match, Andy Murray of Britain survived a second-set lapse to beat Andy Roddick of the United States 6-4, 1-6, 6-1.

Federer also lost his opening match last year before going on to win his fourth Masters Cup title. This time, he was worried about his back.

“I was sort of skeptical going into the match because the practice sessions haven’t been hard at all,” Federer said.

But instead of pain, Federer found rust. He committed 50 unforced errors to just 29 winners. He got in only half of his first serves, which lacked some of their usual sting.

“Definitely it was a factor today,” Federer said, estimating he hit only 50 serves the last nine days. “The shoulder gets a little rusty and things don’t work out the way you want it.

“I don’t know if that cost me the match. I was still in the position to win. It was a pity I couldn’t get to the finish line before him.”

Federer showed flashes of his usual brilliance, then a quick slide downhill.

“Definitely today shots maybe I miss I normally don’t miss,” Federer said. “I think that’s just lack of practice and just uncertainty where my back was today. Now at least I have a match under my belt, especially three sets, and I hope I can play better in the next match.”

Federer gave credit to Simon, who won their only previous meeting, also in three sets, in Toronto in July.

“The better you play, the better he plays,” Federer said.

The ninth-ranked Simon, added to the field when No. 1 Rafael Nadal withdrew with knee tendinitis, capitalized on Federer’s slips. He ripped a backhand crosscourt winner on break point as Federer served at 3-4 in the third set, then served his seventh ace on match point.

“It’s always hard to win against Federer,” Simon said. “I know that I have to play my best tennis. I just wanted to give everything on the court.”

The crowd overwhelmingly favored Federer. Swiss flags were scattered around the nearly packed Qi Zhong stadium, and one section was a sea of red and white.

Federer broke Simon once in the first set and seemed to be headed for a quick victory, but Simon recovered and took the second set despite wasting three break points in the eighth game.

Murray, also appearing at the Masters Cup for the first time, was sharp at the start against Roddick, hitting five aces in his first two service games. He got the only break in the first set as Roddick served at 2-2.

Special feature Masters champions Check out the men who have won the Tennis Masters Cup since 1970. NBCSports.com

“He could always play tennis,” Roddick said. “There’s no question that he’s very confident right now. That’s probably the main difference.”

Then Murray suddenly lost his rhythm as Roddick found his, winning five straight games. Just as quickly as he lost form, Murray found it again. He held at love to go to 5-1, and after Roddick held to take the set, Murray won the first five games of the third.

“Legs don’t quite have the snap in them that they did, you know, a few months ago,” Murray said, referring to the long season on tour. “I’ll try and do my best to recover for the next match.”

Novak Djokovic and Nikolay Davydenko, who won their first matches in the Gold Group, play each other Tuesday after Jo-Wilfried Tsonga and Juan Martin del Potro meet in an earlier match.

Also on NBCSports.com Beyond the Arc: No. 11 Mich. St. takes big step forward Chandler: Jeremy Lin was special even in 8th grade What NFC teams need this offseason  |  And AFC DeMarco: Dodgers could become a contender Follow us on Twitter: @NBCSports  |  And Facebook