ATP Finals: Roger Federer crashes to opening defeat to Dominic Thiem

Switzerland's Roger Federer slipped to an opening straight sets defeat to  Austria's Dominic Thiem in their opening round-robin clash at the ATP Finals in London.

(CNN)Roger Federer's bid for a seventh ATP Finals victory suffered a major setback as he lost his opening round robin match to Austrian Dominic Thiem Sunday at the O2 Arena.

Federer went down 7-5 7-5 to Thiem, who has failed to qualify from the group stages in his three previous appearances at the end of season showpiece.
But the fifth seed went into the ma