New York: Top-ranked defending champion Novak Djokovic fought through shoulder pain to reach the third round of the rain-hit US Open on Wednesday while Roger Federer shook off another slow start to advance.

Djokovic was treated for a sore left shoulder throughout his 6-4, 7-6, 6-1 victory over Argentina's 56th-ranked Juan Ignacio Londero. "It was definitely affecting my serve and backhand," Djokovic said of his shoulder injury.