Defending U.S. Open champion Rafael Nadal sealed his place in the fourth round by defeating Argentina's David Nalbandian in straight sets.

World number two Nadal beat Nalbandian 7-6 (7-5) 6-1 7-5 but was given a stern test in a 62-minute first set.

Nalbandian served for it at 5-4 but the Spaniard produced his best tennis to eventually take it into a tie-break, which he won, according to BBC Sport.