NEW YORK, N.Y. - Top-ranked Serena Williams and Novak Djokovic are seeded No. 1 for the U.S. Open.

The U.S. Tennis Association announced the seedings Tuesday. The year's last major tournament starts Monday, when Williams will seek to complete the first Grand Slam since Steffi Graf in 1988. She has won the U.S. Open each of the previous three times she was seeded No. 1, including the past two years.

Romania's Simona Halep is seeded second, followed by Maria Sharapova and the 2014 runner-up, Caroline Wozniacki.

Two-time runner-up Victoria Azarenka is seeded 20th, while Venus Williams is 23rd.

Roger Federer is seeded second on the men's side, with Andy Murray third and last year's runner-up, Kei Nishikori, fourth.

Rafael Nadal is eighth and defending champ Marin Cilic ninth.