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Federer faces uphill battle at ATP Finals after opening loss

(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 match with a 4-2 career win record over the veteran Federer, who was nonetheless the favorite after his recent tournament victory in Basel.The Swiss 20-time grand slam winner made the worst possible start as he was broken in the first game of the match, but broke back to level in a closely fought opener.Thiem then broke again in the 11th game before serving out to take a one set lead.Federer ...