Rafael Nadal has reached the quarter-finals of the US Open with a straight-sets victory over Luxembourg's Gilles Muller.

The match had been postponed over the last two days after heavy rain in New York, with the Spaniard leading the protests over scheduling at the tournament.

When play was resumed, the number two seed was 0-3 down to his opponent in the first set but managed to take it to a tie-break, which he won 7-1.

On a dry day at Flushing Meadows, Nadal wasted little time in the remaining two sets, dispatching Muller 6-2 6-1.

The defending champion will now face Andy Roddick in the next round after the American beat Nadal's fellow countryman David Ferrer.