LONDON, ENGLAND - NOVEMBER 14: Roger Federer of Switzerland plays a forehand during the singles match against Alexander Zverev of Germany on day three of the Nitto ATP World Tour Finals at O2 Arena on November 14, 2017 in London, England. (Photo by Julian Finney/Getty Images)
LONDON, ENGLAND - NOVEMBER 14: Alexander Zverev of Germany returns the ball during the singles match against Roger Federer of Switzerland on day three of the Nitto ATP World Tour Finals at O2 Arena on November 14, 2017 in London, England. (Photo by Naomi Baker/Getty Images)
LONDON, ENGLAND - NOVEMBER 14: Alexander Zverev of Germany celebrates during the singles match against Roger Federer of Switzerland on day three of the Nitto ATP World Tour Finals at O2 Arena on November 14, 2017 in London, England. (Photo by Julian Finney/Getty Images)
LONDON, ENGLAND - NOVEMBER 14: Roger Federer of Switzerland celebrates victory during the singles match against Alexander Zverev of Germany on day three of the Nitto ATP World Tour Finals at O2 Arena on November 14, 2017 in London, England. (Photo by Julian Finney/Getty Images)
LONDON, ENGLAND - NOVEMBER 14: Alexander Zverev of Germany congratulates Roger Federer of Switzerland on victory following their singles match on day three of the Nitto ATP World Tour Finals at O2 Arena on November 14, 2017 in London, England. (Photo by Clive Brunskill/Getty Images)
