In March 1976, Comăneci competed in the inaugural edition of the American Cup at Madison Square Garden in Manhattan. She received rare scores of 10, which signified a perfect routine without any deductions, for her vault in the preliminary stage and for her floor exercise routine in the final of the all-around competition, which she won. During this competition, Comăneci met American gymnast Bart Conner for the first time. While he remembered this meeting, Comăneci noted in her memoirs that she had to be reminded of it later in life. She was 14 and Conner was celebrating his 18th birthday. They both won a silver cup and were photographed together. A few months later, they participated in the 1976 Summer Olympics that Comăneci dominated, while Conner was a marginal figure. Conner later said, "Nobody knew me, and [Comăneci] certainly didn't pay attention to me."
On July 18, 1976, Comăneci made history at the Montreal Olympics. During the team compulsory portion of the competition, she was awarded the first perfect 10 in Olympic gymnastics for her routine on the uneven bars. But Omega SA, the traditional Olympics scoreboard manufacturer, had been led to believe that competitors could not receive a perfect ten, and had not programmed the scoreboard to display that score. Comăneci's perfect 10 thus appeared as "1.00," the only means by which the judges could indicate that she had received a 10.
Comăneci was the first Romanian gymnast to win the Olympic all-around title. She also holds the record as the youngest ever Olympic gymnastics all-around champion. The sport has revised its age-eligibility requirements. Gymnasts must be at least 16 in the same calendar year of the Olympics in order to compete during the Games. When Comăneci competed in 1976, gymnasts had only to be 14 by the first day of the competition. As a result of changes to age eligibility, Comăneci's record cannot be broken.