Gut was the second to start and benefited from the best visibility on the Oreiller-Killy course that she also considers a favourite. She clocked 1 minute, 19.75 seconds, with American Leanne Smith .16 seconds behind in second place, and Switzerland's Nadja Kamer 0.50 back in third.
"It's my first victory in downhill and it's a pleasure. I'd been second in Val d'Isere before," Gut said. "It feels good, and I feel like I've been skiing well since the start of the season. I already thought in St. Moritz (last weekend) that a podium was coming."
Gut finished third behind Kamer and Vonn in a World Cup downhill at Val d'Isere two years ago, and she also won two silver medals in downhill and super-combined at the 2009 world championships in the Alpine resort.
"When you've done well somewhere you always think you can repeat it, that's what makes the difference," Gut said "It's a shame the world championships won't be here (next year)."
Gut climbed up to fifth in the overall standings.
"I'm still young, I have a lot to learn," Gut said. "I think I'm a long way from winning the overall. But I've already got five years of experience and I have to make the most of that."
Larisa Yurkiw of Owen Sound, Ont., did not finish.
Vonn lost balance and veered to the left, landing heavily into the netting. After a few moments, the American got back up and managed to ski to the bottom unassisted, suggesting she was not seriously injured.
Vonn has won two downhills and two super-Gs this season.
But there was better news for the U.S. ski team as Smith was one of four Americans in the top 10 — with Julia Mancuso seventh; Alice McKennis eighth, and Stacey Cook 10th.
"I'm beyond excited. This is something that you dream about that you put your heart and soul into," Smith said. "Today was my day. I'm really happy with the outcome. I've been on the World Cup team for a few years now and starting to feel comfortable. Hopefully you'll see more of me now."
Overall World Cup leader Tina Maze of Slovenia was 12th. But she extended her lead over Vonn, who was third overall, to 285 points.
Vonn had some cause for optimism because neither Maze nor Hoefl-Riesch, who finished 13th, made significant gains in terms of points. Hoefl-Riesch, who beat Vonn by just three points to win the World Cup two seasons ago, has 463 points to Vonn's 413 so far.
Vonn didn't train well this week, finishing 18th on Wednesday and a shaky 48th on Thursday. She will look to make amends in Saturday's super-G.
"She will be back with a vengeance," Smith said. "I know she will be coming out tomorrow fighting, and showing her best skiing again."
Vonn did not stop for reporters when she got back to the bottom of the course. Before climbing onto a bus, she replied "not feeling great" when asked by The Associated Press if she was OK.
The crash was even more surprising as it came in Vonn's best event.
Before Friday, she had finished in the top five in her last 27 World Cup downhill races, including 17 wins and 24 podiums, and missed only the top five once in 43 downhills since January 2007.
Vonn was aiming for her third straight World Cup downhill win at Val d'Isere.
Kamer, meanwhile, was surprised with her result.
"I thought I would get top 10 when I reached the line," Kamer said. "I never thought I would make the podium, so I'm lucky."