Who was the youngest US Open women's singles champion in the Open Era?

Tracy Austin was the youngest US Open women's singles champion in the Open Era.

Austin won the 1979 US Open at age 16 years and 9 months, defeating four-time defending champion Chris Evert 6–4, 6–3 in the final. She became the youngest woman to win the US Open, a record that still stands for the tournament.

Her victory was remarkable because she also defeated Martina Navratilova in the semifinals before facing Evert. The result ended Evert's attempt to win a fifth consecutive US Open title and made Austin the youngest major champion of the Open Era at that point.

Austin won the US Open again in 1981, beating Navratilova in a three-set final. She later became the youngest person inducted into the International Tennis Hall of Fame, entering in 1992 at age 29. Maria Sharapova, Serena Williams, and Chris Evert were all teenagers or young champions, but none was younger than Austin at the US Open.