NEW YORK -- Defending champion Serena Williams and her sister Venus were among 101 of the top 104 female players in the world officially entered in the U.S. Open on Thursday.

Martina Hingis, the 1997 champion, Anna Kournikova and Tatiana Panova are the three players who withdrew.

Hingis hasn't played in a WTA Tour event since October because of foot injuries and might never compete again but is still ranked 101st. Kournikova, ranked 77th, has been sidelined with a hurt back.

Serena Williams will be aiming to win her sixth title in seven majors. She beat 2000-01 U.S. Open champion Venus in last year's championship match at Flushing Meadows.

Other past major champions on the entry list announced Thursday include Monica Seles, Jennifer Capriati, Lindsay Davenport, Justine Henin-Hardenne, Conchita Martinez, Mary Pierce and Iva Majoli.

The men's entry list, released Wednesday, didn't include defending champion Pete Sampras. He has withdrawn from every tournament since he won his record 14th major title at last year's U.S. Open.

The seedings and draw will be announced during the week before the tournament, which begins Aug. 25.