Simone Biles mixed brilliance with an unfamiliar touch of the erratic as she launched into Tokyo 2020 action, just about keeping alive the prospect of beating her Rio haul of four gold medals.

The American gymnastics great headed the all-around individual standings, just ahead of the impressive Brazilian Rebeca Andrade, with USA team-mate Sunisa Lee in third.

She remains in the hunt in six events, but it was far from a dominant Biles at the Ariake Gymnastics Centre, and the United States team as a whole had an unusually mediocre day. The Russian Olympic Committee gymnasts finished above them in the team standings for the first time since 2010 at a major event.

Russia's score of 171.629 suggested they can post a major challenge in the final to the usually dominant United States (170.562), although Biles and her team-mates will want to prove themselves once again.

Since 2011, the USA have won team gold at all five World Championships and both Olympic Games, in London and Rio.

Biles' landings were not near as sure-footed as they have so typically been, and in her floor exercise she misjudged a tumbling pass to such an extent she stepped back all the way off the raised floor.

Tom Forster, high performance co-ordinator for the USA, was taken aback by Biles' mistakes.

He said: "That was a surprise. She's been incredibly consistent and I'm sure she feels bad, but I'm super proud of the way she trained.

"She's been a great leader for us. Sometimes, just like in other sports, great athletes drop the ball in the end zone or a quarterback throws an interception. It happens. Those steps are mental errors."

At one point it appeared Biles might miss out on the eight-woman final of the uneven bars, but she squeezed in, benefiting from the rule that allows only two athletes from each nation in the final. Biles finished 10th in qualifying, but four Russian competitors were ahead of her, with two of those unable to advance.

It means she remains in the hunt for titles in all six of her events, including the team competition, for which Forster will look to ensure Biles and her team-mates are thoroughly prepared.

"Staying in bounds would help. Simone took three big steps on her beam dismount. I've never seen her do that before," Forster said.

The challenge of the Russian team could lift the Americans, or it could point to a changing of the guard at the top of women's gymnastics.

Forster is only looking to the former, saying: "This might be a great awakening for us, and we'll take advantage of it."

While 24-year-old Biles battles to recover peak form in time for Tuesday's team final, Olympic veteran Oksana Chusovitina has reached the end of the road in her Games career.

Competing at her eighth Olympics, the 46-year-old took part in the vault but failed to qualify for the final.

Chusovitina, who has previously competed for the Soviet Union and Germany and made her Games debut in 1992, was back representing her native Uzbekistan in Tokyo and received an ovation from her rivals after producing two valiant vaults.

"It was really nice. I cried tears of happiness because so many people have supported me for a long time," she said of the recognition.

"I feel very proud and happy. I'm saying goodbye to sports. It's kind of mixed feelings. I'm alive, I'm happy, I'm here without any injuries, and I can stand on my own."