Japan's Kei Nishikori produced a big upset against six-time champion Roger Federer, defeating the Swiss great in straight sets 7-6(4), 6-3 in a first-round group match at the ATP Finals on Sunday.World No. 9 Nishikori had not beaten the third-ranked Federer since 2014 but he reduced his career head-to-head deficit with the 20-time Grand Slam champion to 3-7 with the win at the O2 in London."It was good that I took the first set tie-break and converted the few chances I had in the second set," said Nishikori, who has reached the semifinals of the ATP Finals twice."I don't think of him as an …READ FULL ARTICLE
