Jessica Lindell-Vikarby took first at Cortina d'Ampezza, her first World Cup victory.
Still, Vonn's top-10 finish extended her World Cup lead to 104 points.
"Super G has been a struggle for the last couple years, and I don't really know what's wrong," said Vonn, a Minnesota native who skis out of Vail, Colo.
Her coach, Jim Tracy, said variable snow conditions could have played a role.
"She was not fast on the top. She came down and in the first 14 seconds she was three-tenths out. You really have to execute to make that up," Tracy said. "I think the snow conditions from the first seven women changed and something was different."
The women next compete in Garmisch Partenkirchen, Germany, alongside the men's alpine World Cup tour.