Fans cheer after Juan Martin Del Potro of Argentina beat Robin Soderling of Sweden in a singles semi-final match during the Barclays ATP World Tour Tennis Finals in London, on November 28, 2009. AFP PHOTO/CARL DE SOUZA (Photo credit should read CARL DE SOUZA/AFP/Getty Images)

Juan Martin Del Potro of Argentina celebrates after beating Robin Soderling of Sweden in a singles semi-final match during the Barclays ATP World Tour Tennis Finals in London, on November 28, 2009. AFP PHOTO/IAN KINGTON (Photo credit should read IAN KINGTON/AFP/Getty Images)

Juan Martin Del Potro of Argentina celebrates after beating Robin Soderling of Sweden in a singles semi-final match during the Barclays ATP World Tour Tennis Finals in London, on November 28, 2009. AFP PHOTO/CARL DE SOUZA (Photo credit should read CARL DE SOUZA/AFP/Getty Images)

Juan Martin Del Potro of Argentina celebrates after beating Robin Soderling of Sweden 6-7 (1-7) 6-3 7-6 (7-3) in a singles semi-final match during the Barclays ATP World Tour Tennis Finals in London, on November 28, 2009. AFP PHOTO/CARL DE SOUZA (Photo credit should read CARL DE SOUZA/AFP/Getty Images)

Fans celebrate after Juan Martin Del Potro of Argentina beat Robin Soderling of Sweden 6-7 (1-7) 6-3 7-6 (7-3) in a singles semi-final match during the Barclays ATP World Tour Tennis Finals in London, on November 28, 2009. AFP PHOTO/CARL DE SOUZA (Photo credit should read CARL DE SOUZA/AFP/Getty Images)

Fans with their faces painted celebrate after Juan Martin Del Potro of Argentina beat Robin Soderling of Sweden 6-7 (1-7) 6-3 7-6 (7-3) in a singles semi-final match during the Barclays ATP World Tour Tennis Finals in London, on November 28, 2009. AFP PHOTO/CARL DE SOUZA (Photo credit should read CARL DE SOUZA/AFP/Getty Images)

Juan Martin Del Potro of Argentina celebrates after beating Robin Soderling of Sweden 6-7 (1-7) 6-3 7-6 (7-3) in a singles semi-final match during the Barclays ATP World Tour Tennis Finals in London, on November 28, 2009. AFP PHOTO/IAN KINGTON (Photo credit should read IAN KINGTON/AFP/Getty Images)

Argentina's Juan Martin Del Potro celebrates after beating Sweden's Robin Soderling to win their ATP World Tour Finals semifinal tennis match at the O2 Arena in London, Saturday Nov. 28, 2009.

Juan Martin Del Potro of Argentina celebrates after beating Robin Soderling of Sweden 6-7 (1-7) 6-3 7-6 (7-3) in a singles semi-final match during the Barclays ATP World Tour Tennis Finals in London, on November 28, 2009. AFP PHOTO/IAN KINGTON (Photo credit should read IAN KINGTON/AFP/Getty Images)

Juan Martin Del Potro of Argentina celebrates after beating Robin Soderling of Sweden 6-7 (1-7) 6-3 7-6 (7-3) in a singles semi-final match during the Barclays ATP World Tour Tennis Finals in London, on November 28, 2009. AFP PHOTO/IAN KINGTON (Photo credit should read IAN KINGTON/AFP/Getty Images)

LONDON, ENGLAND - NOVEMBER 28: Juan Martin Del Potro of Argentina celebrates winning the match during the men's singles semi final match against Robin Soderling of Swedenduring the Barclays ATP World Tour Finals at the O2 Arena on November 28, 2009 in London, England. (Photo by Christopher Lee/Getty Images for Barclays ATP Finals)

LONDON, ENGLAND - NOVEMBER 28: Juan Martin Del Potro of Argentina celebrates winning the match during the men's singles semi final match against Robin Soderling of Swedenduring the Barclays ATP World Tour Finals at the O2 Arena on November 28, 2009 in London, England. (Photo by Christopher Lee/Getty Images for Barclays ATP Finals)

Argentina's Juan Martin Del Potro reacts as he plays Sweden's Robin Soderling during their ATP World Tour Finals semifinal tennis match at the O2 Arena in London, Saturday Nov. 28, 2009.

Argentina's Juan Martin Del Potro reacts as he plays Sweden's Robin Soderling during their ATP World Tour Finals semifinal tennis match at the O2 Arena in London, Saturday Nov. 28, 2009.

Juan Martin Del Potro of Argentina plays against Robin Soderling of Sweden in a singles semi-final match during the Barclays ATP World Tour Tennis Finals in London, on November 28, 2009. AFP PHOTO/CARL DE SOUZA (Photo credit should read CARL DE SOUZA/AFP/Getty Images)

LONDON, ENGLAND - NOVEMBER 28: Juan Martin Del Potro of Argentina celebrates winning the match during the men's singles semi final match against Robin Soderling of Swedenduring the Barclays ATP World Tour Finals at the O2 Arena on November 28, 2009 in London, England. (Photo by Clive Brunskill/Getty Images)

Fans cheer for Juan Martin Del Potro of Argentina as he plays against Robin Soderling of Sweden in a singles semi-final match during the Barclays ATP World Tour Tennis Finals in London, on November 28, 2009. AFP PHOTO/CARL DE SOUZA (Photo credit should read CARL DE SOUZA/AFP/Getty Images)

LONDON, ENGLAND - NOVEMBER 28: Juan Martin Del Potro of Argentina celebrates winning the match during the men's singles semi final match against Robin Soderling of Swedenduring the Barclays ATP World Tour Finals at the O2 Arena on November 28, 2009 in London, England. (Photo by Christopher Lee/Getty Images for Barclays ATP Finals)

LONDON, ENGLAND - NOVEMBER 28: Juan Martin Del Potro of Argentina celebrates winning the match during the men's singles semi final match against Robin Soderling of Swedenduring the Barclays ATP World Tour Finals at the O2 Arena on November 28, 2009 in London, England. (Photo by Julian Finney/Getty Images)

LONDON, ENGLAND - NOVEMBER 28: Juan Martin Del Potro of Argentina celebrates winning the match during the men's singles semi final match against Robin Soderling of Swedenduring the Barclays ATP World Tour Finals at the O2 Arena on November 28, 2009 in London, England. (Photo by Julian Finney/Getty Images)

Argentina's Juan Martin Del Potro celebrates after beating Sweden's Robin Soderling to win their ATP World Tour Finals semifinal tennis match at the O2 Arena in London, Saturday Nov. 28, 2009.

Fans cheer for Juan Martin Del Potro of Argentina as he plays against Robin Soderling of Sweden in a singles semi-final match during the Barclays ATP World Tour Tennis Finals in London, on November 28, 2009. AFP PHOTO/CARL DE SOUZA (Photo credit should read CARL DE SOUZA/AFP/Getty Images)

LONDON, ENGLAND - NOVEMBER 28: Juan Martin Del Potro of Argentina celebrates winning the match during the men's singles semi final match against Robin Soderling of Swedenduring the Barclays ATP World Tour Finals at the O2 Arena on November 28, 2009 in London, England. (Photo by Julian Finney/Getty Images)

LONDON, ENGLAND - NOVEMBER 28: Juan Martin Del Potro of Argentina celebrates winning the match during the men's singles semi final match against Robin Soderling of Swedenduring the Barclays ATP World Tour Finals at the O2 Arena on November 28, 2009 in London, England. (Photo by Clive Brunskill/Getty Images)

Juan Martin Del Potro of Argentina gestures as he plays against Robin Soderling of Sweden in a singles semi-final match during the Barclays ATP World Tour Tennis Finals in London, on November 28, 2009. AFP PHOTO/CARL DE SOUZA (Photo credit should read CARL DE SOUZA/AFP/Getty Images)

LONDON, ENGLAND - NOVEMBER 28: Juan Martin Del Potro of Argentina celebrates winning the match during the men's singles semi final match against Robin Soderling of Swedenduring the Barclays ATP World Tour Finals at the O2 Arena on November 28, 2009 in London, England. (Photo by Clive Brunskill/Getty Images)

LONDON, ENGLAND - NOVEMBER 28: Juan Martin Del Potro of Argentina celebrates winning the match during the men's singles semi final match against Robin Soderling of Swedenduring the Barclays ATP World Tour Finals at the O2 Arena on November 28, 2009 in London, England. (Photo by Clive Brunskill/Getty Images)

Juan Martin Del Potro of Argentina puts the ball in his mouth as he plays against Robin Soderling of Sweden in a singles semi-final match during the Barclays ATP World Tour Tennis Finals in London, on November 28, 2009. AFP PHOTO/CARL DE SOUZA (Photo credit should read CARL DE SOUZA/AFP/Getty Images)

Juan Martin Del Potro of Argentina gestures as he plays against Robin Soderling of Sweden in a singles semi-final match during the Barclays ATP World Tour Tennis Finals in London, on November 28, 2009. AFP PHOTO/CARL DE SOUZA (Photo credit should read CARL DE SOUZA/AFP/Getty Images)

Juan Martin Del Potro of Argentina gestures as he plays against Robin Soderling of Sweden in a singles semi-final match during the Barclays ATP World Tour Tennis Finals in London, on November 28, 2009. AFP PHOTO/CARL DE SOUZA (Photo credit should read CARL DE SOUZA/AFP/Getty Images)