BEIJING, Aug. 9 (Xinhua) -- Swiss Roger Federer, who just celebrated his 27th birthday on Friday, will start his bid to capture an Olympic gold medal against Dmitry Tursunov of Russia in the first round on Sunday.

    Federer, who will relinquish his World No. 1 ranking to Rafael Nadal on August 18, has competed at two Olympic Games at Sydney in 2000 and Athens in 2004.

    "Tursunov is a very dangerous player, I have to take care," Federer said on Thursday.

    In 2000 he lost a semifinal to Tommy Haas and then let a bronze medal slip through his fingers against Frenchman Arnaud Di Pasquale. Four years later he lost in the second round to Tomas Berdych.

    "I have won a lot of Grand Slams, but it is a different feeling to play in the Olympics. You carry your country in your mind, you want to do well and that will add extra pressure."

    Federer has avoided a potential third-round meeting with his Cincinnati conqueror, No. 14 seed Ivo Karlovic of Croatia, who is a late withdrawal due to injury.

    The Swiss led 2-0 over Tursunov in career, but both meetings were in 2006 when Federer seemed unbeatable.

    The Russian, 35th-ranked and one year Federer's junior, has enjoyed a consistent season, claiming Sydney title and reaching the final of the ATP Masters event in Indianapolis.

    The Women's part will pit third seed Svetlana Kuznetsova against China's Li Na, seconded seed Serb Jelena Jankovic versus Zimbabwe's Cara Black and fourth seed Serena Williams of the United States against Olga Govortsova of Belarus.

    Li, former world number 20, has been ranked as one of the Olympic hopes after her trailblazing work for China in tennis, but the 26-year-old was suffering injury woes since last year when she was sidelined for half a year. Coming back into the Tour early this year, Li again needed months to rest herself ahead of the Beijing Games.

    "Li used to beat Kuznetsova, but it is hard to say about the result. She has just returned to the court, so I don't know whether she is able to play her game," Chinese head coach Jiang Hongwei said.

    The Russian kept a 3-1 lead over Li. Li beat Kuznetsova at the 2006 Wimbledon where she finally reached last eight.

    Williams, an eight-time Grand Slam champion, is making her singles debut in Olympics. Having missed Athens Games with a knee injury, Williams this time is still nursing an injury which has tortured her for months.

    "I love playing for my country. This is the Olympics, and of all my trophies, a gold medal is my favourite. For me, this is as big as the U.S Open," said Williams, who claimed the women's doubles title with her sister Venus in Sydney 2000.

    Elsewhere, Nadal and world number three Novak Djokovic will play respective men's doubles matches while Spain's fifth seed David Ferrer and Russian Nicolay Davydenko will be tested in the men's singles on Sunday.