The 31-year-old Curtoni took advantage of being the second skier down the mountain, posting an error-free run that none of her rivals could touch as conditions worsened throughout the race in this International Ski and Snowboard Federation event.

Curtoni's teammate Sofia Goggia came second, at 0.29 seconds, despite injuring her hand during her run, while Olympic downhill champion Corinne Suter of Switzerland was third at 0.73sec behind.

It was Curtoni's second World Cup downhill win after her triumphs in Bankso, Bulgaria, in January 2020 and in the World Cup super-G on home snow in Cortina d'Ampezzo last January.

"I'm really happy," Curtoni said in the finish area.

"With flat light it's tough and you need to be brave.

"I think I was able to put all my braveness on the slope today and it went well."

Following more than 20 centimetres of overnight snow in St. Moritz, the start gate was lowered to the super-G start, removing nine gates from the downhill course.

Snow continued to fall throughout the race, while fog drifted in and out of the Corviglia course as the racers took their turns.

Curtoni set the early mark and watched on as several skiers shortly after her, including Michelle Gisin of Switzerland, Romane Miradoli of France, who did not finish, and Breezy Johnson of the United States made mistakes on a sharp left turn near the top of the course that put paid to their chances.

Suter and Goggia, the last two Olympic downhill gold medallists, used their considerable skill and experience to successfully navigate the tricky turn and find their way on to the podium, but they did not seriously challenge Curtoni's time.

Goggia hit the third control gate with her left hand but she still managed to record the fastest speed of the race at 99.45 kilometres an hour and add second place to her twin victories in the Canadian resort of Lake Louise earlier this month.

Post-race scans revealed she suffered a fracture of the second and third metacarpals in her hand and she was to undergo immediate surgery in Milan in order to try to start tomorrow's downhill race.

Suter was unable to win her first World Cup race on home snow in Switzerland, but she still recorded her third downhill podium in as many attempts this season after finishing second and third behind Goggia in Lake Louise.

"I didn't feel very, very comfortable so I tried to find the risk today," she said.

"You can't see the bumps and it's not so easy but I tried my best and when it stays like this (third place), I'm super happy."

Suter's teammate Jasmine Flury came fourth as the first skier down the mountain, missing the podium by 11 hundredths of a second.

Racing continues throughout the weekend in St. Moritz with another downhill tomorrow and a super-G on Sunday (December 18) as Curtoni looks to build on today's victory in better conditions.

"Tomorrow we're going to start from zero because it's going to be sunny and we're going to start from the top," she said.

"It's a new race, it's a new day, and I'm looking forward to it."