Caroline Wozniacki of Denmark was seeded No 1 at a Grand Slam tournament for the first time on Tuesday, receiving the top spot at the US Open because Serena Williams pulled out with an injured foot.

Wozniacki, ranked No 2 behind Williams by the WTA, was the runner-up at Flushing Meadows last year and is the first woman since 2003 to be seeded No 1 at the US Open without having won a major championship.

Defending champion Kim Clijsters was seeded No 2 by the US Tennis Association, which stuck strictly to the rankings in determining the seedings. Venus Williams, the 2000 and 2001 US Open champion, is No 3, followed by 2008 runner-up Jelena Jankovic and French Open runner-up Samantha Stosur.

Two other past US Open champions who received seed were No 11 Svetlana Kuznetsova and No 14 Maria Sharapova.

Serena Williams, Venus' younger sister, withdrew last week, saying she was recovering from surgery to repair cuts on her right foot.

The men's seedings were announced on Monday, with Rafael Nadal at No 1 and Roger Federer at No 2. The 2009 men's champion, Juan Martin del Potro of Argentina, withdrew on Saturday because he said he was not ready to compete after having an operation on his right wrist in May.

The announcement of the women's seedings was delayed a day because Sunday's final at the Rogers Cup in Montreal was rained out. Wozniacki wound up winning Monday's final for her third title of the year.

The draw for the US Open is on Thursday, and play begins on Monday.