Mary Lou Piatek-Daniels (born August 6, 1961) is a retired tennis player from the U.S. who played on the WTA Tour during the 1980s.

In 1979, she was the no. 1 junior in the world. She won her first pro title at Richmond, Virginia 1981, beating Sylvia Hanika and Sue Barker en route. She was coached by her father Joseph, a former varsity player at Indiana University, and by Trinity coach Emilie Foster.

Piatek-Daniels made her ranking debut in February 1980 at no. 45. Her career wins include Robin White, Christiane Jolissaint, Kathy Horvath, Wendy White, Gigi Fernández, and Betsy Nagelsen.^[1]

Result	W/L	Date	Tournament	Surface	Opponent	Score
Loss	1.	Jul 1980	Richmond, Virginia, US	Carpet	Martina Navratilova	3–6, 0–6
Win	2.	Aug 1981	Richmond, Virginia, US	Carpet	Sue Barker	6–4, 6–1
Loss	3.	Sep 1981	Atlanta, Georgia, US	Carpet	Tracy Austin	6–4, 3–6, 3–6
Win	4.	Jan 1984	Denver, Colorado, US	Hard	Kim Sands	6–1, 6–1

Result	W/L	Date	Tournament	Surface	Partner	Opponents	Score
Loss	1.	Dec 1980	Tucson, Arizona, US	Carpet	Wendy White	Leslie Allen Barbara Potter	6–7, 0–6
Loss	2.	Feb 1981	Houston, Texas, US	Carpet	Regina Maršíková	Sue Barker Ann Kiyomura	7–5, 4–6, 3–6
Win	3.	Oct 1981	Deerfield Beach, Florida, US	Hard	Wendy White	Pam Shriver Paula Smith	6–1, 3–6, 7–5
Loss	4.	Feb 1982	Kansas City, Missouri, US	Carpet	Anne Smith	Barbara Potter Sharon Walsh	6–4, 2–6, 2–6
Loss	5.	Oct 1982	Tampa, Florida, US	Hard	Wendy White	Ann Kiyomura Paula Smith	2–6, 4–6
Win	6.	Jan 1983	Marco Island, Florida, US	Clay	Andrea Jaeger	Rosie Casals Wendy Turnbull	7–5, 6–4
Loss	7.	Nov 1983	Deerfield Beach, Florida, US	Hard	Pam Casale	Bonnie Gadusek Wendy White	1–6, 6–3, 3–6
Loss	8.	Jan 1984	Nashville, Tennessee, US	Hard	Paula Smith	Sherry Acker Candy Reynolds	7–5, 6–7, 6–7
Loss	9.	Mar 1984	Boston, Massachusetts, US	Carpet	Andrea Leand	Barbara Potter Sharon Walsh	6–7, 0–6
Loss	10.	Oct 1984	Tarpon Springs, Florida, US	Hard	Wendy White	Carling Bassett Liz Smylie	4–6, 3–6
Win	11.	Jan 1985	Denver, Colorado, US	Carpet	Robin White	Leslie Allen Sharon Walsh	1–6, 6–4, 7–5
Loss	12.	Sep 1985	New Orleans, Louisiana, US	Carpet	Anne White	Chris Evert-Lloyd Wendy Turnbull	1–6, 2–6
Win	13.	Oct 1985	Indianapolis, Indiana, US	Hard	Bonnie Gadusek	Penny Barg Sandy Collins	6–1, 6–0
Loss	14.	Mar 1987	Phoenix, Arizona, US	Hard	Anne White	Penny Barg Beth Herr	6–2, 2–6, 6–7
Win	15.	Mar 1987	Dallas, Texas, US	Carpet	Anne White	Elise Burgin Robin White	7–5, 6–3
Win	16.	Nov 1987	Little Rock, Arkansas, US	Hard	Robin White	Lea Antonoplis Barbara Gerken	6–2, 6–4
Loss	17.	Apr 1989	Hilton Head, South Carolina, US	Clay	Wendy White	Hana Mandlíková Martina Navratilova	4–6, 1–6
Loss	18.	Feb 1990	Hilton Head, South Carolina, US	Clay	Wendy White	Manon Bollegraf Meredith McGrath	0–6, 2–6
Win	19.	Feb 1990	Oklahoma City, Oklahoma, US	Hard	Wendy White	Manon Bollegraf Lise Gregory	7–5, 7–2
Loss	20.	Apr 1991	Hilton Head, South Carolina, US	Clay	Lise Gregory	Claudia Kohde-Kilsch Natalia Zvereva	4–6, 0–6
Loss	21.	Nov 1991	Indianapolis, Indiana, US	Hard	Sandy Collins	Katrina Adams Elna Reinach	7–5, 2–6, 4–6

• Mary Lou Piatek-Daniels at the Women's Tennis Association
• Mary Lou Piatek-Daniels at the International Tennis Federation