World Cup champion Shiffrin won the slalom in front of Sweden's Anna Swenn Larsson (+0.16), with Petra Vlhova (+0.20) from Slovakia taking third place.
"It’s the first race of the season and I’m feeling good with my skiing, my skis felt amazing," the American said.
"It was a nice feeling on the first run, I felt pretty good, but I was holding back a little bit.
"On the second run I made adjustments and it felt like a really good pace and tempo. I was strong and solid everywhere.”
It was Shiffrin's fifth victory on the Levi Black piste.