France's Nastasia Noens was second and Canadian Marie-Michele Gagnon finished third.
Shiffrin, 20, returned to skiing only two weeks ago after injuring ligaments in her right knee while training in Sweden in early December.
"A good comeback day," she told the fis-ski.com website.
"That was a pretty incredible race and it’s weird. I’m kind of glad it’s over, but I also enjoyed skiing that last run. It was really rough and it was a challenge every single gate."
The victory was Shiffrin's 18th in her World Cup career and third this season in the technical discipline after winning twice in Aspen.
Shiffrin won the slalom at the 2013 and 2015 world championships and the 2014 Sochi Olympics.
Sweden's Frida Hansdotter leads the World Cup slalom standings with 545 points to 446 for Veronika Velez-Zuzulova of Slovakia. Shiffrin is sixth with 300.
(Reporting by Alan Baldwin, editing by Ed Osmond)
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