Olympics: Lee grabs all-around gold for US as Biles watches on

With Biles watching from the front row at the Ariake Gymnastics Centre, Lee clinched gold in the all-around to secure the title for the United States' for a fifth consecutive Games on the final rotation - the floor exercise - to post a winning total of 57.433.

Surprise package, 22-year-old Brazilian Rebeca Andrade, who had topped the rankings most of the evening, grabbed the silver for her country's first ever medal in women's gymnastics.

Russian Angelina Melnikova completed the podium by taking the bronze for the ROC.

Jade Carey, who was tapped to fill in placed eighth.

Considered heir apparent to Biles, 18-year-old Lee's moment arrive sooner than expected.

Biles, winner of every all-around competition she entered since 2013, threw the fight for the Olympic gold wide open when she decided not to defend her Rio Games all-around title.

Biles had already dropped out of the team event on Tuesday after one poor vault, citing the need to focus on her mental health.

It all added up to another thriller at the Ariake arena that has seen almost every medal decided by the final athlete in the final rotation.

As the gymnasts marched over to the floor only 0.201 separated the top three of Lee, Andrade and 16-year-old Russian Vladislava Urazova, leaving everything to play for.

Lee, the youngest member of the U.S. team, put down a marker in the floor exercise with a score of 13.700 but she had left the door open a crack for Andrade to snatch the gold.

But the Brazilian, who had looked so poised, finally cracked by stepping out on her first tumbling run and then did so a second time, scoring 13.666, with the mistakes likely costing her the gold.