Serena Williams was 17 years old when she won her first Grand Slam singles title. She captured the 1999 US Open women’s singles championship on September 11, defeating world No. 1 Martina Hingis 6–3, 7–6.
Williams was born on September 26, 1981, so she had not yet turned 18 when the final was played. The victory came during only her second full year on the professional tour and marked her breakthrough at the sport’s highest level.
The 1999 US Open was different from her first professional singles title, which she won earlier that year at the Open Gaz de France in Paris. It was also her first Grand Slam singles crown, while she and Venus Williams won the women’s doubles title at the same tournament.
Some accounts confuse the tournament year with her age at the time or round her age up to 18. The precise answer is 17.