Versatile player well known for her upset of Serena Williams to reach the semifinals of the 2013 Australian Open. She won her first Grand Slam title at the 2017 US Open.
She started playing tennis at the Sierra Sport and Racquet Club in Fresno, California, when she was 9 years old.
She turned professional in 2010.
She was born to John Stephens and Sybil Smith, whom were both athletes. She got engaged to soccer player Jozy Altidore in April 2019.
In her Australian Open victory over Serena Williams, she won 90 percent of her points at the net.