There were also upsets in the tennis, with Wimbledon champion Ashleigh Barty knocked out, and the taekwondo where Britain's two-time champion Jade Jones lost in the first round.
Even favourite Simone Biles was wobbly in gymnastics qualifying, while golf was robbed of two leading players through positive Covid-19 tests and defending tennis champion Andy Murray pulled out of the men's singles.
And in basketball, the USA had their 25-game winning streak at the Olympics ended by an 81-76 loss to France in their opening game.
But the biggest shock of the day must surely have been for Dutch cyclist Annemiek van Vleuten, who celebrated when she crossed the line thinking she had won gold only to discover she was in fact second.
Amid all the surprises, there was the reassuring return to action of Japanese tennis player Naomi Osaka and it was more about thrills as skateboarding and surfing made their Olympic debuts.