Novak Djokovic has claimed that there is not a favourite for his quarter-final encounter with Juan Martin del Potro at the US Open.
The defending champion, who beat Stanislas Wawrinka in the last round, takes on the Argentine at Flushing Meadows this evening for a place in the semi-finals.
"Del Potro is a quality player, somebody that when he's physically fit he can challenge anybody on any surface," Djokovic said.
"It's quarter-finals. There is no really clear favourite anymore. I have to try to play my best."
The pair recently met in the bronze-medal match at the London Olympics, with Del Potro winning that contest in straight sets.
