Early bird Novak Djokovic into US Open last 16

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Defending champion Novak Djokovic reached the US Open last 16 for the sixth successive year on Sunday, coasting past Frenchman Julien Benneteau 6-3, 6-2, 6-2 despite being forced to open up play for the day.

The second-seeded Serb, kicking off the day-seven programme on Arthur Ashe Stadium, didn't face a single break point in his 97-minute victory, his fourth on the trot against Benneteau, firing 13 aces and 41 winners.

The 25-year-old Djokovic, who hasn't dropped serve since the first game of his first-round match, goes on to face either Swiss 18th seed Stanilas Wawrinka or 14th-seeded Ukrainian Alexander Dolgopolov for a spot in the quarter-finals.

"It was an early match for me. Usually I don't like to play the first match," said Djokovic.

"So it was important to stay strong and commit to every point."

Later Sunday, Spanish fourth seed David Ferrer tackles Australian wildcard Lleyton Hewitt, the 2001 champion, in a battle of two of the eight men over 30 who made the third round.

The last time there were eight players over 30 at this stage in New York was in 1974.

Ferrer has five titles to his name in 2012 -- second only to Roger Federer's six -- and is enjoying his best year in the Grand Slams, making the semi-finals at the French Open and the last eight at the Australian Open and Wimbledon.

The winner of that tie will have a last-16 date with either French 13th seed Richard Gasquet or US national college champion Steve Johnson, the world number 245.

Argentine seventh seed Juan Martin del Potro, the champion in 2009, faces compatriot Leonardo Mayer.

Del Potro's win in New York three years ago was the only occasion in the last 30 majors that the champion wasn't Roger Federer, Rafael Nadal or Djokovic.

The winner of that clash could face 2003 champion Andy Roddick, playing his last tournament before retirement, or colourful Italian Fabio Fognini for a quarter-final slot.

Elsewhere, Serb eighth seed Janko Tipsarevic, a quarter-finalist in 2011, takes on Slovenian qualifier Grega Zemlja with the winner to face either US ninth seed John Isner or German 19th seed Philipp Kohlschreiber.