A time of 1:37.08 saw her edge out Sofia Goggia by just 0.05secs, with downhill table-topper Ilka Stuhec in third.
Gut has now sealed nine World Cup podium finishes this season across all disciplines, and sits second in the overall standings on 1023 points.
Vonn had arrived in Italy on the back of her 77th World Cup win in the downhill at Garmisch-Partenkirchen last week in only her second race since breaking her right arm in November and fracturing her left knee last February.
Meanwhile, the most successful female skier of all time Lindsey Vonn suffered another crash exactly at the same spot of the course where she wiped out the day earlier in an official training session.
In the men's downhill at Garmisch-Partenkirchen, there was another surprise victor as Austrian Hannes Reichelt went out on the course first, setting a time 1:53.83 which ended up being too quick to beat.
The four-time overall World Cup victor returned earlier this month from almost a year out with knee and arm injuries.
He now has 279 points, leapfrogging Norwegian Kjetil Jansrud after he finished fifth today.
Gut's compatriot Beat Feuz was third.
Tomorrow, the women will contest a super-G race while the men are in giant slalom action.