The four-time Olympic champion exited the final at the Ariake Gymnastics Centre after a less than impressive opening vault.
The United States of America is the most successful nation in the history of the Olympic Games.
The 24-year-old Biles will be the oldest American women's gymnast since 26-year-old Annia Hatch and Mohini Bhardwaj, 25, in the 2004 Olympics.
She is one of America's greatest Olympians and is considered one of the greatest of all time in the sport.