Kei Nishikori of Japan reacts after the group match with Stan Wawrinka of Switzerland at the 2016 ATP World Tour Final at O2 in London, Britain on Nov. 14, 2016. Nishikori won 2-0. (Xinhua/Han Yan)
Stan Wawrinka of Switzerland returns a shot during the group match with Kei Nishikori of Japan at the 2016 ATP World Tour Final at O2 in London, Britain on Nov. 14, 2016. Nishikori won 2-0. (Xinhua/Han Yan)
Kei Nishikori of Japan returns a shot in the group match with Stan Wawrinka of Switzerland at the 2016 ATP World Tour Final at O2 in London, Britain on Nov. 14, 2016. Nishikori won 2-0. (Xinhua/Han Yan)
Kei Nishikori of Japan returns a shot in the group match with Stan Wawrinka of Switzerland at the 2016 ATP World Tour Final at O2 in London, Britain on Nov. 14, 2016. Nishikori won 2-0. (Xinhua/Han Yan)
Stan Wawrinka of Switzerland returns a shot during the group match with Kei Nishikori of Japan at the 2016 ATP World Tour Final at O2 in London, Britain on Nov. 14, 2016. Nishikori won 2-0. (Xinhua/Han Yan)
Kei Nishikori of Japan returns a shot in the group match with Stan Wawrinka of Switzerland at the 2016 ATP World Tour Final at O2 in London, Britain on Nov. 14, 2016. Nishikori won 2-0. (Xinhua/Han Yan)
Kei Nishikori of Japan reacts after the group match with Stan Wawrinka of Switzerland at the 2016 ATP World Tour Final at O2 in London, Britain on Nov. 14, 2016. Nishikori won 2-0. (Xinhua/Han Yan)
