American teenager Sunisa Lee won the women's gymnastics all-around Olympic gold on Thursday, succeeding defending champion Simone Biles who withdrew over concerns for her mental health.

Lee, 18, won ahead of Rebeca Andrade, the first Brazilian woman to win an artistic gymnastics medal, with Russian women's team gold medallist Angelina Melnikova in the bronze medal position.

Her trek to the top of the podium in Tokyo has not been without enormous personal trauma - in 2019 her father was paralysed from the chest down after a fall from a ladder and last year her aunt and uncle perished from Covid-19.

She said: "The past two years with Covid have been crazy. There was one point I wanted to quit. To be here and to be an Olympic gold medallist is just crazy." 

The Olympic debutante was adding gold to the silver she won as part of the US women's team on Tuesday with a points tally of 57.433, 0.144 clear of Andrade, with Melnikova 0.099 away in third.

The crown was dramatically left undefended when Biles dropped out of the in-running team competition on Tuesday and subsequently the all-around.

In the normal course of events Biles would have been hot favourite to become the first back-to-back winner in over half a century.

Few would have bet against that outcome in a discipline where she is undefeated since 2013 -- an era of domination that has delivered 19 world championship golds to go with her Brazilian quartet.

But fate in the form of an attack of the "twisties" left Biles as a mere bystander, with the spotlight normally trained on her instead illuminating the face of her smiling compatriot.

It was the fourth final in four days to go down to the final rotation, with Lee's polished floor exercise earning 13.7 to go into provisional gold, with Andrade unable to dislodge her.

Andrade it was who led after the top six in qualifying had visited the vault, with the Brazilian devotee of Beyonce conjuring up an impressive one and a half twisted Cheng, and on the button on the landing too.

And after a clean routine on the uneven bars she held a narrow 0.066 point cushion over the chasing group led by Lee.

But a strong beam routine pushed Lee into the lead going into the concluding floor exercise, with Andrade initially lying third but promoted into second after a tenth of a point was added to her difficulty rating following an inquiry.

Lee had gold in her grasp after her floor routine with Andrade unable to prevent her becoming the fifth consecutive American winner of the all-around.