Roger Federer slumped to a shock straight sets defeat in his opening round-robin clash against Kei Nishikori at the ATP Finals in London on Sunday.
Federer, appearing at the ATP showpiece for the 16th time looking for a seventh title and a first since 2011, finds himself up against it now after losing 7-6 (7-4) 6-3 as Nishikori moved level with Kevin Anderson at the top of Group Lleyton Hewitt.
Nishikori, who suffered two recent losses against Federer in Shanghai and Paris, is known as one of the game's quicker returners and was keeping pace with the Swiss in an erratic encounter which required a first set tie-break.
A frustrated Federer handed his opponent the lead and the Japanese star eventually took his opportunity with his fourth set point to make it a winning 17-5 record in breakers for the season.
Federer lost narrowly to Novak Djokovic in Paris last week but headed to the capital in confident mood. But after two early breaks of serve from both players, it was Nishikori took advantage of tightness creeping into the 37-year-old's arm to break through in the sixth game.
Nishikori, who is making his fourth appearance at the season finale, having reached the semi-finals in 2014 and 2016, served out the match having struck just six winners in the entire contest.
Shot of the match
Nishikori had the O2 Arena wowing in amazement following a sumptuous backhand winner at full stretch.
Winners reaction
"It's never easy playing against my idol, and now it's always a big challenge for me to play against Roger," said Nishikori. It was great to win today. I had to change something today because I lot to him twice recently so I think I used my forehand more and played aggressive. Things worked for me, especially in the second set."
Experts' view
What's next
Kevin Anderson takes on Kei Nishikori and Roger Federer will take on Dominic Thiem in Tuesday's matches.
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