![LONDON, ENGLAND - NOVEMBER 14: Roger Federer of Switzerland serves 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)](https://thenational-the-national-prod.cdn.arcpublishing.com/resizer/v2/JMEEET6CET7NG3UQXUTXTKVBBM.jpg?smart=true&auth=b0fbe6109ea3398ec68793154e0286811fe1ae9dc1cd03eb0e3a90e3618c46b5&width=400&height=225)
Roger Federer of Switzerland defeated Alexander Zverev. Photo by Julian Finney/Getty Images
Roger Federer of Switzerland defeated Alexander Zverev. Photo by Julian Finney/Getty Images
Federer pleased to 'show that quality of mine' to beat Zverev and reach last four of ATP World Tour Finals
Swiss master wins 7-6, 5-7, 6-1 and looks like a top contender to win season-ending tournament