Barclays ATP World Tour Finals - Day Two(01 of20)
Open Image ModalLONDON, ENGLAND - NOVEMBER 05: Novak Djokovic of Serbia walks out for his men's singles match against Roger Federer of Switzerland during day two of the Barclays ATP World Tour Finals at O2 Arena on November 5, 2013 in London, England. (Photo by Clive Brunskill/Getty Images) (credit:Getty Images)
Barclays ATP World Tour Finals - Day Two(02 of20)
Open Image ModalLONDON, ENGLAND - NOVEMBER 05: Novak Djokovic of Serbia walks out for his men's singles match against Roger Federer of Switzerland during day two of the Barclays ATP World Tour Finals at O2 Arena on November 5, 2013 in London, England. (Photo by Clive Brunskill/Getty Images) (credit:Getty Images)
Barclays ATP World Tour Finals - Day Two(03 of20)
Open Image ModalLONDON, ENGLAND - NOVEMBER 05: Novak Djokovic of Serbia volleys in his men's singles match against Roger Federer of Switzerland during day two of the Barclays ATP World Tour Finals at O2 Arena on November 5, 2013 in London, England. (Photo by Jan Kruger/Getty Images) (credit:Getty Images)
Barclays ATP World Tour Finals - Day Two(04 of20)
Open Image ModalLONDON, ENGLAND - NOVEMBER 05: Novak Djokovic of Serbia serves in his men's singles match against Roger Federer of Switzerland during day two of the Barclays ATP World Tour Finals at O2 Arena on November 5, 2013 in London, England. (Photo by Clive Brunskill/Getty Images) (credit:Getty Images)
Barclays ATP World Tour Finals - Day Two(05 of20)
Open Image ModalLONDON, ENGLAND - NOVEMBER 05: Novak Djokovic of Serbia serves in his men's singles match against Roger Federer of Switzerland during day two of the Barclays ATP World Tour Finals at O2 Arena on November 5, 2013 in London, England. (Photo by Clive Brunskill/Getty Images) (credit:Getty Images)
Barclays ATP World Tour Finals - Day Two(06 of20)
Open Image ModalLONDON, ENGLAND - NOVEMBER 05: Novak Djokovic of Serbia hits a forehand in his men's singles match against Roger Federer of Switzerland during day two of the Barclays ATP World Tour Finals at O2 Arena on November 5, 2013 in London, England. (Photo by Clive Brunskill/Getty Images) (credit:Getty Images)
Barclays ATP World Tour Finals - Day Two(07 of20)
Open Image ModalLONDON, ENGLAND - NOVEMBER 05: Novak Djokovic of Serbia hits a forehand in his men's singles match against Roger Federer of Switzerland during day two of the Barclays ATP World Tour Finals at O2 Arena on November 5, 2013 in London, England. (Photo by Clive Brunskill/Getty Images) (credit:Getty Images)
TENNIS-ATP-FINALS(08 of20)
Open Image ModalSerbia's Novak Djokovic celebrates beating Switzerland's Roger Federer in their group B singles match in the round robin stage on the second day of the ATP World Tour Finals tennis tournament in London on November 5, 2013. Djokovic won 6-4, 6-7, 6-2. AFP PHOTO / BEN STANSALL (Photo credit should read BEN STANSALL/AFP/Getty Images) (credit:Getty Images)
Barclays ATP World Tour Finals - Day Two(09 of20)
Open Image ModalLONDON, ENGLAND - NOVEMBER 05: Roger Federer of Switzerland congratulates Novak Djokovic of Serbia after their men's singles match during day two of the Barclays ATP World Tour Finals at O2 Arena on November 5, 2013 in London, England. (Photo by Clive Brunskill/Getty Images) (credit:Getty Images)
Barclays ATP World Tour Finals - Day Two(10 of20)
Open Image ModalLONDON, ENGLAND - NOVEMBER 05: Novak Djokovic of Serbia signs autographs for fans after victory in his men's singles match against Roger Federer of Switzerland during day two of the Barclays ATP World Tour Finals at O2 Arena on November 5, 2013 in London, England. (Photo by Julian Finney/Getty Images) (credit:Getty Images)
Barclays ATP World Tour Finals - Day Two(11 of20)
Open Image ModalLONDON, ENGLAND - NOVEMBER 05: Novak Djokovic of Serbia celebrates victory in his men's singles match against Roger Federer of Switzerland during day two of the Barclays ATP World Tour Finals at O2 Arena on November 5, 2013 in London, England. (Photo by Clive Brunskill/Getty Images) (credit:Getty Images)
Barclays ATP World Tour Finals - Day Two(12 of20)
Open Image ModalLONDON, ENGLAND - NOVEMBER 05: Novak Djokovic of Serbia celebrates victory in his men's singles match against Roger Federer of Switzerland during day two of the Barclays ATP World Tour Finals at O2 Arena on November 5, 2013 in London, England. (Photo by Clive Brunskill/Getty Images) (credit:Getty Images)
TENNIS-ATP-FINALS(13 of20)
Open Image ModalSerbia's Novak Djokovic celebrates beating Switzerland's Roger Federer in their group B singles match in the round robin stage on the second day of the ATP World Tour Finals tennis tournament in London on November 5, 2013. Djokovic won 6-4, 6-7, 6-2. AFP PHOTO / GLYN KIRK (Photo credit should read GLYN KIRK/AFP/Getty Images) (credit:Getty Images)
Barclays ATP World Tour Finals - Day Two(14 of20)
Open Image ModalLONDON, ENGLAND - NOVEMBER 05: Novak Djokovic of Serbia celebrates victory in his men's singles match against Roger Federer of Switzerland during day two of the Barclays ATP World Tour Finals at O2 Arena on November 5, 2013 in London, England. (Photo by Clive Brunskill/Getty Images) (credit:Getty Images)
Barclays ATP World Tour Finals - Day Two(15 of20)
Open Image ModalLONDON, ENGLAND - NOVEMBER 05: Novak Djokovic of Serbia celebrates victory in his men's singles match against Roger Federer of Switzerland during day two of the Barclays ATP World Tour Finals at O2 Arena on November 5, 2013 in London, England. (Photo by Clive Brunskill/Getty Images) (credit:Getty Images)
TENNIS-ATP-FINALS(16 of20)
Open Image ModalSerbia's Novak Djokovic celebrates beating Switzerland's Roger Federer in their group B singles match in the round robin stage on the second day of the ATP World Tour Finals tennis tournament in London on November 5, 2013. Djokovic won 6-4, 6-7, 6-2. AFP PHOTO / BEN STANSALL (Photo credit should read BEN STANSALL/AFP/Getty Images) (credit:Getty Images)
TENNIS-ATP-FINALS(17 of20)
Open Image ModalSerbia's Novak Djokovic celebrates beating Switzerland's Roger Federer in their group B singles match in the round robin stage on the second day of the ATP World Tour Finals tennis tournament in London on November 5, 2013. Djokovic won 6-4, 6-7, 6-2. AFP PHOTO / BEN STANSALL (Photo credit should read BEN STANSALL/AFP/Getty Images) (credit:Getty Images)
Barclays ATP World Tour Finals - Day Two(18 of20)
Open Image ModalLONDON, ENGLAND - NOVEMBER 05: Novak Djokovic of Serbia hits a forehand in his men's singles match against Roger Federer of Switzerland during day two of the Barclays ATP World Tour Finals at O2 Arena on November 5, 2013 in London, England. (Photo by Michael Regan/Getty Images) (credit:Getty Images)
Barclays ATP World Tour Finals - Day Two(19 of20)
Open Image ModalLONDON, ENGLAND - NOVEMBER 05: Novak Djokovic of Serbia shows his frustration in his men's singles match against Roger Federer of Switzerland during day two of the Barclays ATP World Tour Finals at O2 Arena on November 5, 2013 in London, England. (Photo by Clive Brunskill/Getty Images) (credit:Getty Images)
Barclays ATP World Tour Finals - Day Two(20 of20)
Open Image ModalLONDON, ENGLAND - NOVEMBER 05: Novak Djokovic of Serbia hits a forehand in his men's singles match against Roger Federer of Switzerland during day two of the Barclays ATP World Tour Finals at O2 Arena on November 5, 2013 in London, England. (Photo by Clive Brunskill/Getty Images) (credit:Getty Images)