Switzerland's Fatton wins women's ski mountaineering sprint on Olympic debut
Fatton clocked a winning time of 2min 59.77sec on the Stelvio course, depriving France's four-time World Cup champion Emily Harrop by 2.38sec.
Spain's Ana Alonso Rodriguez claimed bronze, 10.45sec down on Fatton's pace.
Harrop, a four-time World Cup overall champion, had been hot favourite in skimo, an adrenaline-packed sprint requiring athletes to negotiate uphill climbs on ski and foot before descending by ski.
But she paid the price for a slow second transition.
After an initial ascent, Harrop was neck-and-neck with Fatton as the pair took off their skis to climb a stairway on foot.
Skiers have to re-don their skis at the top for one final climb, and Fatton was much slicker than Harrop, racing away to a lead she never looked likely to relinquish.