Nadal sees off Kiefer

Third seed Nadal, still making his way back from an eight-week injury lay-off due to knee problems that left him unable to defend his Wimbledon title, had looked to be cruising to victory after taking the first set without the loss of a game.

He had not counted on the determination of his German opponent who made him fight for the remainder of the match before Nadal ran out a 6-0 3-6 6-3 6-4 winner at Arthur Ashe Stadium.

The victory means Nadal will next play fellow Spaniard and 32nd seed Nicolas Almagro, a five-set winner over American Robbie Ginepri and also completed a second round in which all of the top 16 seeds progressed to the last 32.

"I'm very happy to be in the next round," Nadal said. "I feel good, I started well, he started slow and later he played better.

"When you win the first set easy and like that and he starts to play better it's difficult. Nicolas is a great player, he played a good match and I'm very happy to beat him."

Sixth seed Juan Martin Del Potro stayed on course for a quarter-final meeting with Andy Murray when he advanced with a three-set win over Jurgen Melzer, although his overall performance was inconsistent.

The Argentinian was pushed all the way in a first set lasting more than an hour before winning 8-6 on a tie-break. Although he won the following two sets 6-3, last year's quarter-finalist produced four double faults and 36 unforced errors.

Jo-Wilfried Tsonga, seventh seed, also enjoyed a straight-sets win over Finland's Jarkko Nieminen.

While he had five double faults, the Frenchman won 92% of his points on his first serve and served 11 aces to win 7-5 6-3 6-4 and will next play compatriot Julien Benneteau, who eliminated 30th seed Victor Troicki of Romania, 6-1 3-6 6-1 6-0.