LONDON - Defending champion Rafael Nadal was named Wimbledon top seed on Wednesday ahead of five-times winner Roger Federer.

Wimbledon officials employ a unique seeding system where they take into account previous results at the grasscourt championships and there was a strong case for Federer to be named top seed because he has contested the last six finals.

But the committee opted to stick to the world rankings with Andy Murray, Novak Djokovic, Juan Martin del Potro and Andy Roddick completing the top six.

Russia's Marat Safin was the main beneficiary after being bumped up from his world ranking of 23rd to 15th seed following his unexpected run to the semi-finals 12 months ago.

Wimbledon is the only grand slam tournament which does not stick strictly to the ATP ranking list in deciding seedings. In allocating the slots the seeding's committee takes into account performances on grass over a two-year period.

Former women's champion Maria Sharapova has also been boosted up to 24th seed despite being ranked 59th. The Russian returned to the tour last month after a nine-month layoff with a shoulder injury and she has been rewarded for impressive record at the All England Club.

The women's top 16 seedings have stuck rigidly to the world rankings with Dinara Safina, Serena Williams and Venus Williams heading the field.

Wimbledon begins on Monday and the draw takes place on Friday.