Girmay, who was already the first Black African to win a grand tour stage at the 2022 Giro d'Italia, timed his effort to perfection to beat Colombian Fernando Gaviria and Belgian Arnaud de Lie, second and third respectively.
Ecuador's Richard Carapaz took the overall leader's yellow jersey.
Pre-stage favourite Jasper Philipsen of Belgium was involved in a huge crash with 2.3km left of the stage.
Girmay is more than just a sprinter, and was aided in his victory by the absence of stage favourite Philipsen.
He signalled his coming of age in 2022 when he became the first African to win a one-day classic at Gent-Wevelgem, aged 21.
It was his second Grand Tour stage win after the Giro d'Italia in 2022 where he injured an eye opening a bottle of prosecco on the podium.
More to follow.
