The four-times overall World Cup champion completed the course in one minute 4.36 seconds and showed no signs of the back pain which troubled her in St Mortiz last week.
It was the 78th World Cup race win of Vonn's career but the first since the downhill at Garmisch in January.
Vonn finished 0.31 seconds ahead of Italy's Sofia Goggia with Norway's Ragnhild Mowinckel in third.
"I had a bad start to the season, and now I'm at a much better level, this win is very important for me," she told Swiss television, adding that she would also race in another Super G on Sunday.
"I hope the weather helps tomorrow and we can have a good race."
Liechtenstein's Tina Weirather, third in the overall World Cup standings at the start, crashed on a steep curve high on the course but skied away unharmed.
Switzerland's Lara Gut, recovering from an anterior cruciate knee injury, was ninth.
(Writing by Brian Homewood in Bern, editing by Pritha Sarkar)
