Britain Tennis ATP Finals(01 of22)
Open Image ModalJapanâs Kei Nishikori waves to the crowd as he leaves after being defeated in his ATP World Tour Finals semifinal tennis match against Serbiaâs Novak Djokovic at the O2 Arena in London Saturday, Nov. 15, 2014. (AP Photo/Tim Ireland) (credit:ASSOCIATED PRESS)
Britain Tennis ATP Finals(02 of22)
Open Image ModalJapanâs Kei Nishikori plays a return to Serbiaâs Novak Djokovic during the ATP World Tour Finals semifinal tennis match at the O2 Arena in London Saturday, Nov. 15, 2014. (AP Photo/Tim Ireland) (credit:ASSOCIATED PRESS)
Britain Tennis ATP Finals(03 of22)
Open Image ModalJapanâs Kei Nishikori looks dejected during the ATP World Tour Finals semifinal tennis match against Serbiaâs Novak Djokovic at the O2 Arena in London Saturday, Nov. 15, 2014. (AP Photo/Tim Ireland) (credit:ASSOCIATED PRESS)
Britain Tennis ATP Finals(04 of22)
Open Image ModalJapanâs Kei Nishikori plays a return to Serbiaâs Novak Djokovic during the ATP World Tour Finals semifinal tennis match at the O2 Arena in London Saturday, Nov. 15, 2014. (AP Photo/Tim Ireland) (credit:ASSOCIATED PRESS)
Britain Tennis ATP Finals(05 of22)
Open Image ModalSerbiaâs Novak Djokovic plays a return to Japanâs Kei Nishikori during the ATP World Tour Finals semifinal tennis match at the O2 Arena in London Saturday, Nov. 15, 2014. (AP Photo/Tim Ireland) (credit:ASSOCIATED PRESS)
Britain Tennis ATP Finals(06 of22)
Open Image ModalSerbiaâs Novak Djokovic serves to Japanâs Kei Nishikori during the ATP World Tour Finals semifinal tennis match at the O2 Arena in London Saturday, Nov. 15, 2014. (AP Photo/Tim Ireland) (credit:ASSOCIATED PRESS)
Britain Tennis ATP Finals(07 of22)
Open Image ModalSerbiaâs Novak Djokovic plays a return to Japanâs Kei Nishikori during the ATP World Tour Finals semifinal tennis match at the O2 Arena in London Saturday, Nov. 15, 2014. (AP Photo/Tim Ireland) (credit:ASSOCIATED PRESS)
Britain Tennis ATP Finals(08 of22)
Open Image ModalSerbiaâs Novak Djokovic celebrates after defeating Japanâs Kei Nishikori during their singles ATP World Tour Finals semifinal tennis match at the O2 Arena in London, Saturday, Nov. 15, 2014. (AP Photo/Kirsty Wigglesworth) (credit:ASSOCIATED PRESS)
Britain Tennis ATP Finals(09 of22)
Open Image ModalJapanâs Kei Nishikori celebrates after he wins a point against Serbiaâs Novak Djokovic during their singles ATP World Tour Finals semifinal tennis match at the O2 Arena in London, Saturday, Nov. 15, 2014. (AP Photo/Kirsty Wigglesworth) (credit:ASSOCIATED PRESS)
Britain Tennis ATP Finals(10 of22)
Open Image ModalJapanâs Kei Nishikori plays a return to Serbiaâs Novak Djokovic during their singles ATP World Tour Finals semifinal tennis match at the O2 Arena in London, Saturday, Nov. 15, 2014. (AP Photo/Kirsty Wigglesworth) (credit:ASSOCIATED PRESS)
Britain Tennis ATP Finals(11 of22)
Open Image ModalJapanâs Kei Nishikori plays a return to Serbiaâs Novak Djokovic during their singles ATP World Tour Finals semifinal tennis match at the O2 Arena in London, Saturday, Nov. 15, 2014. (AP Photo/Kirsty Wigglesworth) (credit:ASSOCIATED PRESS)
Britain Tennis ATP Finals(12 of22)
Open Image ModalSerbiaâs Novak Djokovic plays a return to Japanâs Kei Nishikori during their singles ATP World Tour Finals semifinal tennis match at the O2 Arena in London, Saturday, Nov. 15, 2014. (AP Photo/Kirsty Wigglesworth) (credit:ASSOCIATED PRESS)
Britain Tennis ATP Finals(13 of22)
Open Image ModalJapanâs Kei Nishikori plays a return to Serbiaâs Novak Djokovic during their singles ATP World Tour Finals semifinal tennis match at the O2 Arena in London, Saturday, Nov. 15, 2014. (AP Photo/Kirsty Wigglesworth) (credit:ASSOCIATED PRESS)
Britain Tennis ATP Finals(14 of22)
Open Image ModalJapanâs Kei Nishikori plays a return to Serbiaâs Novak Djokovic during their singles ATP World Tour Finals semifinal tennis match at the O2 Arena in London, Saturday, Nov. 15, 2014. (AP Photo/Tim Ireland) (credit:ASSOCIATED PRESS)
Britain Tennis ATP Finals(15 of22)
Open Image ModalJapanÃs Kei Nishikori plays a return to Spain\'s David Ferrer during their ATP World Tour tennis finals match at the O2 arena in London, Thursday, Nov. 13, 2014. (AP Photo/Kirsty Wigglesworth) (credit:ASSOCIATED PRESS)
Britain Tennis ATP Finals(16 of22)
Open Image ModalJapanâs Kei Nishikori celebrates winning against Spain\'s David Ferrer during their ATP World Tour tennis finals match at the O2 arena in London, Thursday, Nov. 13, 2014. (AP Photo/Kirsty Wigglesworth) (credit:ASSOCIATED PRESS)
Britain Tennis ATP Finals(17 of22)
Open Image ModalJapanâs Kei Nishikori celebrates winning against Spain\'s David Ferrer during their ATP World Tour tennis finals match at the O2 arena in London, Thursday, Nov. 13, 2014. (AP Photo/Kirsty Wigglesworth) (credit:ASSOCIATED PRESS)
Britain Tennis ATP Finals(18 of22)
Open Image ModalJapanâs Kei Nishikori changes his shirt after winning a game during his ATP World Tour tennis finals match against Spain\'s David Ferrer at the O2 arena in London, Thursday, Nov. 13, 2014. (AP Photo/Kirsty Wigglesworth) (credit:ASSOCIATED PRESS)
Barclays ATP World Tour Finals - Day Seven(19 of22)
Open Image ModalLONDON, ENGLAND - NOVEMBER 15: Kei Nishikori of Japan in action during the round robin singles match against Novak Djokovic of Serbia on day seven of the Barclays ATP World Tour Finals at O2 Arena on November 15, 2014 in London, England. (Photo by Justin Setterfield/Getty Images) (credit:Justin Setterfield via Getty Images)
Barclays ATP World Tour Finals - Day Seven(20 of22)
Open Image ModalLONDON, ENGLAND - NOVEMBER 15: Novak Djokovic of Serbia towels down in the singles semi-final match against Kei Nishikori of Japan on day seven of the Barclays ATP World Tour Finals at O2 Arena on November 15, 2014 in London, England. (Photo by Clive Brunskill/Getty Images) (credit:Clive Brunskill via Getty Images)
Barclays ATP World Tour Finals - Day Seven(21 of22)
Open Image ModalLONDON, ENGLAND - NOVEMBER 15: Novak Djokovic of Serbia reacts during the round robin singles match against Kei Nishikori of Japan on day seven of the Barclays ATP World Tour Finals at O2 Arena on November 15, 2014 in London, England. (Photo by Justin Setterfield/Getty Images) (credit:Justin Setterfield via Getty Images)
Barclays ATP World Tour Finals 2014: Novak Djokovic vs Kei Nishikori(22 of22)
Open Image ModalLONDON, ENGLAND - NOVEMBER 15: Novak Djokovic of Serbia gestures during the men\'s singles semi-final match with Japan\'s Kei Nishikori on Barclays ATP World Tour Finals at O2 Arena in London, England on November 15, 2014. (Photo by Yunus Kaymaz/Anadolu Agency/Getty Images) (credit:Anadolu Agency via Getty Images)