Novak Djokovic says he "did not feel that great" as he came back from a set down to beat American qualifier Zachary Svajda and reach the US Open third round.

Novak Djokovic delivered a lesson in grand slam tenacity to Learner Tien in the first round of the US Open, beating the American teenager 6-1, 7-6 (3), 6-2

Djokovic, who hasn’t won a Grand Slam title in two years, was far from his best against Learner Tien in New York.