Roger Federer admits tournament struggles caught up with him in US Open defeat to Del Potro

Roger Federer conceded he was not in the right shape to challenge for another grand slam title as the elusive US Open clash with Rafael Nadal slipped away again.

After the Spaniard defeated Andrey Rublev, it seemed virtually nailed on that New York would witness a first meeting between the great beasts of men's tennis in the semi-finals.