Armitstead broke away with Emma Johansson (Wiggle-High5) in the final stages of the hilly cobbled Classic in Oudenaarde and outlasted the Swedish champion in the sprint for the line.
Just two seconds later, three of Armitstead’s teammates crossed the line, with Chantal Blaak, Megan Guarnier and Ellen Van Dijk claiming third, fourth and sixth respectively.
Defending champion and Johansson’s teammate Elisa Longo Borghini finished fifth in the fifth Women’s WorldTour race of the season.
Armitstead has now won four of her six starts this season, including three wins in the WorldTour. The Flanders win takes her back to the top of the Women’s WorldTour rankings, 25 points ahead of Blaak and 83 ahead of Johansson.
The next race on the WorldTour calendar is the Fleche Wallonne Feminine on April 20.