The 2010 giant slalom Olympic champion beat snow and fog to clock one minute and 16.45 seconds and snatch her second win in the discipline after the World Cup finals in Schladming last year.
Rebensburg, who also won a giant slalom in Are last month and now has 10 World Cup race wins, beat second-placed Austrian Nicole Schmidhofer by 0.33 seconds.
"Obviously the conditions were special but I think I skied a pretty good run. In the end, only the result matters and it's a good one to take before the world championships", said the German.
Schmidhofer, 23, timed her first podium finish perfectly to boost her chances of being selected for the national team at the world championships on home snow in Schladming in two weeks' time.
World Cup overall leader Tina Maze finished third, 0.01 behind Schmidhofer, for her 15th podium in 23 races this winter.
"I was not feeling too well and I skied a controlled, precise race. I'm proud of being on the podium in these conditions", said the Slovenian, on course for the record of 18 podiums in a season held by Liechtenstein's Hanni Wenzel since 1980.
Maze, now leading Germany's Maria Hoefl-Riesch by 718 points in the overall World Cup standings - the equivalent of seven victories with only 14 races left - is the only skier ever to have scored top three placings in six different disciplines in the same season.
"Tina is an inspiration because she comes from the giant slalom like me. I hope to become an all-rounder myself in the future," said Rebensburg.
American Lindsey Vonn, winner of Saturday's downhill on the same course, finished seventh, 0.83 off the pace.
The women's circuit moves to Maribor next week, a home weekend for Maze, who made it clear it was one of her main goals of the season.
"To race in front of my home crowd as the World Cup leader will be one of the highlights of the season for me. I'm really looking forward to it," she said.
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