Shiffrin clocked a combined time of two minutes and 3.51 seconds to beat Switzerland's Lara Gut-Behrami (31) by 0.10 seconds. It was back-to-back victories for Shiffrin, who also won on Tuesday.
She will have a chance to complete a treble on Thursday, in the slalom race at the same location.
Shiffrin leads the overall World Cup standings by 305 points from Italy's Sofia Goggia (30).