Mabel Cahill won the singles tennis title by defeating reigning champion Ellen Roosevelt 6–4, 6–1, 4–6, 6–3 in the Challenge Round of the 1891 U.S. Women's National Singles Championship. Cahill had won the right to challenge Ellen Roosevelt by defeating her sister Grace Roosevelt 6–3, 7–5 in the final of the All Comers' competition. The event was played on outdoor grass courts and held at the Philadelphia Cricket Club in Chestnut Hill, Philadelphia from June 23 through June 27, 1891.
|1891 U.S. National Championships|
|Score||6–4, 6–1, 4–6, 6–3|
The event is notable for its change from a best-of-three to a best-of-five format in the final round, a format that continued until 1901, excluding 1893. This was, and still is, unusual for a women's tournament, and was the only stretch of time where a best-of-five format was played at a women's grand slam event.
All Comers' finalsEdit
|Preliminary Round||First round||Semi-finals||Finals|
|Emma Leavitt Morgan||0||0|
|Helen Day Harris||5||6||6||Helen Day Harris||6||3||4|
|Fannie K. Gregory||6||5||1||Grace Roosevelt||3||5|
- Collins, Bud (2016). The Bud Collins History of Tennis (3rd ed.). New York: New Chapter Press. p. 494. ISBN 978-1-937559-38-0.
- Gibbs, Lindsay (27 May 2016). "Why Women Don't Play Best-Of-Five Matches At Grand Slams". Think Progress. Retrieved 17 January 2022.