Rafael Nadal and Ana Ivanovic, both ranked world number one, were named on Tuesday as the top seeds for the US Open which begins at Flushing Meadows on Monday.
It is the first time that Spaniard Nadal, who replaced Roger Federer at the top of the men's rankings on Monday, has been the top seed at a Grand Slam tournament.
Federer, who has won the US Open in each of the past four years, is seeded second, the first time he has not been the top seed in a Grand Slam since the Australian Open of 2004.
Novak Djokovic, the Australian Open champion and runner-up to Federer last year in New York, is seeded third, with Spaniard David Ferrer fourth.
French Open champion Ivanovic, chasing her first US Open title, heads the women's list for the first time, with fellow Serbian Jelena Jankovic at number two.
Former champion Svetlana Kuznetsova of Russia is seeded three, ahead of American Serena Williams.
Olympic champion Elena Dementieva is seeded fifth, with French Open and Olympic Games runner-up Dinara Safina sixth and Wimbledon champion Venus Williams at seven.
The draws for the final Grand Slam event of the year will be made on Thursday.