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 in the round-robin match as the Japanese seventh seed prevailed 7-6 (7/4), 6-3.