Bronzini launched her sprint with 150 meters to go with Vos unable to catch her on the line as Italy won their fourth women’s title in the last five years.
“I believed in my chances, a podium, but I thought that the victory would not be possible,” Bronzini told a news conference.
“I didn’t have a great season. Last year I was not the team’s first option while this year I was. I had more pressure and it makes victory even sweeter.”
Germany’s Ina-Yoko Teutenberg finished third ahead of Briton Nicole Cooke, who produced her effort too late to repeat her 2008 success.
It was Vos’s fifth second place in succession and her 2006 victory is a distant memory.
“I couldn’t believe it could be possible to get silver five times in a row,” said Vos, who broke into tears on the podium.
“I left it too late and when I started my sprint it was close, but not close enough.”
Canadian Clara Hughes, who won two bronze medals in the 1996 Olympics in road cycling and four medals in long track speed skating, including one gold, over the last three Winter Games, briefly looked set for a stunning win when she broke away with more than 30 km left.
But she was reeled in after the Dutch team increased the pace at the head of the bunch and set up a massive sprint that Bronzini won in a carbon copy of last year’s finish.
