Kriechmayr finished in a time of 1:54.68, 0.40 seconds ahead of Canadian James Crawford (25) while Aleksander Aamodt Kilde (30) took third place, 0.68 seconds behind Kriechmayr.
"It is fantastic to have the toughest race behind me, I made a good run. I tried to keep pushing from the start to the end, and it worked really well," Kriechmayr said.
Norwegian Kilde was the favourite to win the race. However, he was not able to claim his fourth downhill victory of the season and lost the opportunity to significantly narrow the overall World Cup gap to leader Marco Odermatt (25) from Switzerland.
"I charged and did my game plan. I maybe could have been a bit faster at the very top but the middle part was good.
"In the bottom I was a little tight on the gate, got squeezed a little bit and lost some momentum.
"That's it, it happens. It was rough conditions but what Vincent (Kriechmayr) did today was incredible," Kilde said.
Odermatt, who came fourth, is the overall World Cup leader with 846 points, 261 points ahead of second-placed Kilde.
The World Cup continues with the super-G event in Bormio on Thursday.
