Rafael Nadal of Spain returns a shot to Gilles Simon...

Rafael Nadal of Spain returns a shot to Gilles Simon of France during the U.S. Open, Sunday. (Sept. 5, 2010) Credit: Getty Images

 Nadal, the top men's seed, had his most efficient performance of the tournament so far, dispatching Gilles Simon 6-4, 6-4, 6-2, to reach the fourth round.

Nadal will face countryman Feliciano Lopez, the No. 23 seed, who advanced when Sergiy Stakhovsky retired with a foot injury at 6-3, 4-0 for Lopez.

Nadal is part of an all-Spanish quarter of the men's draw, with Lopez, Fernando Verdasco and David Ferrer; Albert Montanes makes five men from Spain in the round of 16.

Nadal, vying for his first Open and third Slam of the year, has not been dominating, merely businesslike, in his three matches, despite not losing a set. Lopez is a fellow left-hander and won the most recent meeting between the two, at the Wimbledon tune-up Queen's Club in June.

PHOTOS: 2010 U.S. Open

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