The gold medal favourites – including Megan Rapinoe – boasted a 44-game unbeaten streak going into the game, which included their 2019 World Cup triumph, but also a 1-1 draw with the Swedes earlier this year.
That Stockholm warning was not heeded on their opening fixture on the second day of competition and USA were convincingly beaten by the 2016 silver medallists – who eliminated them on penalties at the last Games in Rio.
Striker Stina Blackstenius scored twice, either side of half-time, before substitute Lina Hurtig added a third.
Team GB also started their campaign off with a win, defeating Chile 2-0.
Tokyo Olympics 2020, delayed from last year due to the Covid-19 pandemic, officially begin with Friday’s opening ceremony, however football and softball events have an earlier start on the schedule.
Germany won the gold medal for women’s football in 2016, defeating Sweden 2-1 in Rio.