Vonn, seeking a 77th career win, has been involved in a cat-and-mouse battle with Gut for the crystal globe for this season's best all-round skier.
But it was not to be for the American in bright, freezing conditions in La Thuile, Vonn's battle to ride through a rough corner misfiring as a ski unclipped itself to send the 31-year-old cartwheeling, unhurt, down the slope.
Gut had previously timed one minute 35.57 seconds down the 2.5-kilometre-long Tre Franco Berthod piste, Austrian Cornelia Huetter taking second 1.02 seconds behind, just one-hundredth of a second faster than Italy's Nadia Fanchini in third.
Gut's victory, her 18th on the World Cup circuit and sixth this season, saw her nab 100 points that took her to a total of 1,073pts in the overall standings, 13 ahead of Vonn.
Germany's Viktoria Rebensburg stands third with 852.
Vonn, who remains atop the downhill standings ahead of second-placed Huetter with Gut in fourth, will have the opportunity to claw back some valuable points in her battle with Gut in Saturday's second downhill, with a super-G also scheduled for Sunday.