Roger Federer suffered a shock straight-sets defeat to Kei Nishikori at the ATP Finals on Sunday, severely denting his bid for the 100th title of his illustrious career.

The Swiss, who has won the season-ending event a record six times, produced an uncharacteristically error-prone and fractious display as the Japanese seventh seed prevailed 7-6 (7/4), 6-3.
The result means Federer is now in danger of failing to qualify for the semi-finals for just the second time in his career.

Federer, 37, has beaten Nishikori in Paris and Shanghai in recent weeks but despite having the backing of a full house at the O2 Arena, he never really settled into a groove.

The normally cool Swiss was warned by the umpire for ball abuse in the 12th game after Nishikori produced a staggering backhand winner down the line.

The Swiss great made 20 unforced errors in the first set and Nishikori capitalised, forcing a tie-break in which he raced to a 6/1 lead before sealing it 7/4.

Federer, showing real urgency, broke Nishikori immediately at the start of the second set but it proved a false dawn as he lost his own serve as his frustrations mounted.

Nishikori broke again in the sixth game and served out for victory