The women's singles' rules have undergone several changes since the first edition. From 1887 to 1911, the event started with a knockout phase, the All-Comers singles, whose winner faced the defending champion in a challenge round.[5]The All-Comers winner was awarded the title six times (1888, 1893, 1898, 1901, 1904, 1907) in the absence of the previous year's champion. The challenge round system was abolished with the 1912 edition.[6] Since 1887, all matches were played as the best-of-three sets, except during the years of 1891, 1892, 1894, and 1896-1901, when it was scored the best-of-five-sets.[6] Before 1887, the winner of the next game at five-games–all took the set in every match except the All-Comers final and the challenge round, which were won by the player who had at least six games and at least two games more than his opponent. This advantage format was introduced for the final sets of early rounds in 1884 for men but for women starting in 1887, and used for all sets in all rounds from 1887 to 1969.[6] The tie-break system was introduced in 1970 for all sets, in its best-of-nine points sudden death version until 1974, and in its best-of-12 points lingering death version since 1975.[6][7][8] In addition, the US Open is the only slam to have a final third set tie-break, which has occured twice in 1981 and in 1985.[3] The court surface changed twice, from grass (1887–1974), to Har-Tru clay (1975–1977), to hard courts, since 1978.[9]
The champion receives a full-size replica of the event's trophy engraved with her name.[10] In 2009, the winner received prize money of US$1,600,000.[11] A bonus pool of $1,000,000 is also to US Open champions who have clinched the first place of the US Open Series.[12] In the U.S. National Championships, Elisabeth Moore (1896, 1901, 1903, 1905) holds the record for most victories with four and Hazel Hotchkiss Wightman (1909–1911) holds the record for most consecutive titles in the women's singles during the challenge round format at three. After the challenge round ended at the U.S. National Championships, Molla Bjurstedt Mallory (1915–1918) and Helen Jacobs (1932–1935) holds the all-time record for most consecutive titles with four, and the most overall was eight wins by Molla Bjurstedt Mallory (1915–1918, 1920–1922, 1926).[3] In the US Open, Chris Evert (1975–1978) holds the record for most consecutive wins at four, and the record for most overall wins at six (1975–1978, 1980, 1982),[3]
Steffi Graf is a five-time champion, and won five over a nine year timespanMartina Navratilova is a four-time champion, and won these twice back-to-backBillie Jean King is a four-time champion overall and a three-time champion in the open era, and won three in four year timespanSerena Williams is a three-time champion, and won these over a ten year timespan