“I have decided not to compete at the Masters Cup in Shanghai,” the statement said.
Nadal retired during his Paris Masters quarterfinal against Nikolay Davydenko on Friday because of a knee injury.
The top-seeded Russian lost the opening set 6-4 before coming back 6-4, 6-1 against the sixth-seeded American.
"I won this mental battle,'' Petrova said.
In the doubles final, Germany's Anna-Lena Groenefeld and American Vania King topped Jill Craybas of the U.S. and Tamarine Tanasugarn of Thailand 7-6 (3), 6-4.
It was the second doubles title this year for both players.
Tsonga produced a stunning display of serving and shot-making to beat defending champion David Nalbandian of Argentina 6-3, 4-6, 6-4 and become the first Frenchman since Sebastien Grosjean in 2001 to win the indoor tournament.
"I think tomorrow I'll be in some pain, especially after the party I'm going to have,'' Tsonga said.
Buoyed by his success at the Bercy indoor arena in Paris, Tsonga now heads to China with his eyes fixed on the prize.
"I think the Masters will be a very important moment for me,'' Tsonga said. "Maybe another great victory could replace this one. Why not? I'm going to give my best.''
Tsonga lost the Australian Open final to Novak Djokovic, but beat the Serb in Paris, and also in the final when he won his first career title in Bangkok, Thailand in October.
Nalbandian's form heading into Sunday's final had looked imperious, but it dipped at the wrong time against Tsonga.
"I think he served better than me and that was pretty much the key of the match,'' Nalbandian said. "I didn't play badly, but I didn't play like the other days. I couldn't move naturally.''
The 13th-seeded Tsonga clinched victory when Nalbandian hit the ball into the net after having missed three break points to pull back to 5-5.
"I was playing with 15,000 people. Everybody was behind me today. The crowd was magic,'' Tsonga said. "Sometimes I had to calm them down because I was perturbed. It was so fabulous.''
The eighth-seeded Nalbandian was gracious in defeat.
"He's a great player and has played brilliantly all week,'' Nalbandian said. "He deserves this title.''
Tsonga joins seven other players in Shanghai, starting Nov. 9, while Nalbandian missed his chance to qualify.
Nalbandian had only four aces compared to 25 for Tsonga.
"Sometimes I couldn't return his serves,'' Nalbandian said. "He won the first set so easily, so fast. Then everything was hard for me.''
Tsonga broke Nalbandian's serve for a 2-1 lead in the deciding set, and saved a break point in the sixth game with an ace.
Nalbandian's frustration showed in the eighth game when he slammed his racket to the ground. But he kept his composure to hold serve in the ninth game and then had Tsonga down 0-40. However, Tsonga saved all three breakpoints, then hit an ace to set up match point and get the crowd on their feet.
Tsonga's first serve flew into the net, but his second pinned Nalbandian to the back of the court and he went on to win the resulting rally.
The win kept the eighth-seeded Argentine on course for a place in the season-ending Masters Cup and a 10th career title.
Nalbandian is one of four players chasing the final two spots for the prestigious tournament in Shanghai. James Blake and Jo-Wilfried Tsonga, who played their semifinal match later Saturday, are also in contention.
Davydenko's strong resistance finally cracked in the seventh game of the deciding set when the Russian lost his serve and Nalbandian held his easily for a 5-3 lead.
Nalbandian won on his second match point when Davydenko's return sailed long.
The sixth-seeded Davydenko lost the first set in 28 minutes, winning just four points on Nalbandian's serve as the Argentine won 79 percent of points on his first serve. Davydenko made 13 unforced errors, mostly from the back of the court.
The Russian picked up his game in the second set, improving his serve and pinning Nalbandian to the baseline with accurate forehands.
Nalbandian found himself under pressure on serve at 6-5 down in the 12th game. He double-faulted and lost the second set when he hit the ball into the net after Davydenko had returned his weak second serve.
Petrova also secured the second alternate berth for next week's season-ending WTA Tour Championships in Doha. The Russian has played in the elite event twice previously.
Petrova advances to play American Angela Haynes, who lost in qualifying but made the draw when Flavia Pennetta withdrew. Fifth-seeded local Aleksandra Wozniak will meet No. 6-seed American Bethanie Mattek in the other semifinal.
Mattek ended the fine run of 17-year-old countrywoman Melanie Oudin 7-6 (7), 6-1, and Haynes ousted French veteran Nathalie Dechy 2-6, 7-6 (2), 6-3 to reach her first WTA Tour semifinals.
David Nalbandian and French hope Jo-Wilfried Tsonga won to also keep up their chances of reaching the Masters Cup.
Nadal retired with a knee injury after losing the first set 6-1 against sixth-seeded Nikolay Davydenko, just hours after Federer pulled out against 11th-seeded James Blake with a sore back.
“I definitely had more than enough chances tonight, so this one will probably stick with me,” Roddick said. “Credit to him, he came up with probably six or seven volleys that were pretty tough on break points.”
In Saturday’s semifinals, defending champion Nalbandian meets 2006 champ Davydenko, and Blake will try to stop Tsonga from becoming the first French winner since Sebastien Grosjean in 2001.
“I think it’s about the best moment in my life on a court,” said Tsonga, who lost the Australian Open final to Novak Djokovic.
Tsonga felt Roddick was slacking at times.
“Sometimes he was giving up on a point where I thought he could have gone and get it,” Tsonga said.
Nadal received a lengthy massage on his right thigh at 4-1 down to try and loosen the muscles around his right knee but was unable to start the second set.
“When I push with the right leg all the time the knee wasn’t there, the knee is going down,” Nadal said. “I felt a sharp, acute pain.”
The Spaniard felt nagging knee pains earlier this week, and it got worse on Friday morning.
“Today when I woke up I felt it a lot. I try to practice but still feel it,” Nadal said. “Later I went to the doctor and the doctor gave me some anti-inflammatories.”
The top-ranked Nadal said he has never had a similar injury and that he needs more tests before he decides whether to play the season-ending Masters Cup, which begins on Nov. 9 in Shanghai.
“Hopefully it’s going to be fine for Shanghai, but you never know,” Nadal said.
Federer withdrew injured from an ATP tournament for the first time, but said his back complaint wasn’t serious.
“My back has been stiff for the last couple of days and I woke up this morning and it did not respond to the treatment I had last night,” Federer said on his Web site.
He said he’s scheduled to fly to Shanghai on Monday but will delay it if he’s uncomfortable. However, he was positive he would be OK.
Nalbandian was close to his best against Murray, who had won at Madrid and Cincinnati and was trying to become the first man to win three consecutive Masters.
“I played almost perfect,” Nalbandian said. “I think I return really well and that’s important in indoor (tennis).”
Nalbandian’s sharp volleying and clever drop shots helped him win 21 of 25 points at the net.
“I’m obviously disappointed to lose, but I’m glad that I played against a guy as good as him,” Murray said. “He probably returned better than me and created a few more chances.”
Although Nalbandian lost his serve twice in the second set, he kept pressuring Murray’s serve and broke him four times.
Tsonga saved 10 break points in the second set against Roddick, and edged the American 15-14 in aces.
His victory eliminated countryman Gilles Simon from claiming the last two berths in the eight-man Masters Cup.
Blake will qualify if he beats Tsonga. Tsonga can qualify if he beats Blake and Nalbandian loses his semifinal.
Juan Martin del Potro was still in Masters Cup contention.
"My back has been stiff for the last couple of days and I woke up this morning and it did not respond to the treatment I had last night,'' Federer said on his Web site Friday. "As a precaution and because I would be unable to play at 100 percent tonight, I have unfortunately had to take the difficult decision not to play.''
Federer apologized to the disappointed fans who came to watch him at the Bercy indoor arena.
Federer said he hopes the injury will only take a few days to recover and that he will be able to play in the season-ending Masters Cup in Shanghai which begins Nov. 9.
"Usually the back is something that takes a few days and it's better again,'' Federer said. "I'm confident and I'm positive that hopefully it's going to get better in the next few days.''
The 13-time Grand Slam champion has never reached the semifinals at the Bercy indoor arena after losing in the 2002 and 2003 quarterfinals.
The 11th-seeded Blake now advances to the last four, where he will face either No. 7 Andy Roddick or No. 13 Jo-Wilfried Tsonga, who played later.
Federer said he first felt a surge of pain when serving during his second-round match against Robin Soderling on Wednesday. The pain subsided overnight but came back in the third round against Marin Cilic when he lunged to retrieve a shot.
"Usually overnight and maybe with painkillers you sort of get over it, but I just feel like I just can't play the way it is right now,'' Federer said. "I mean, you can hit balls but you can't play professional tennis against the best in the world.''
