After her struggles three years ago at the Tokyo Games, Biles made a dazzling Olympic return with a stunning beam routine in gymnastics qualifying.
There were concerns over the four-time Olympic champion as, after producing another impressive performance on the floor, she appeared to be limping.
The 27-year-old came back out for the vault with heavy strapping to her left ankle but came through that routine – and the final apparatus – unscathed and finished top of the all-around standings with three sub-divisions to go.
US coach Cecile Landi later told reporters Biles had “just a little pain in her calf”.
Rapper Snoop Dogg, who is part of the coverage team for American broadcaster NBC, and singer Ariana Grande were at the Bercy Arena to cheer on their compatriot, as was film star Tom Cruise who delighted fans by posing for pictures.
It was a good day for the British gymasts too, as the women qualified for the team final on Tuesday.