Roger Federer’s hopes of winning a record-extending seventh ATP Finals title suffered a blow as Kei Nishikori stunned the Swiss great 7-6(4) 6-3 in their round-robin opener on Sunday.
The 37-year-old began calmly enough but his usually smooth game began to fray towards the end of the first set and fell apart in an error-strewn second.
Unsurprisingly the match ended with a Federer mis-hit, his 34th unforced error of a scrappy display.
Nishikori went 6-1 ahead in the first set tiebreak and although Federer clawed back to 6-4, a forehand into the net allowed the Japanese to take the opener.
Federer, who had qualified for the season-ender for the 16th time, cut a disgruntled figure at times and was even given a warning for swiping a ball high into the stands in the opener.
Nishikori, twice a semi-finalist in London, grew in confidence and broke in the sixth game of the second set for a 4-2 lead when Federer was left flat-footed.
Serving at 5-3 Nishikori might have expected a Federer fightback but it never materialised as he held serve easily to join Kevin Anderson at the top of the Lleyton Hewitt group.