Despite battling a virus and with rain falling on the course, the 22-year-old American completed the two runs in an aggregate time of one minute 47.40 seconds, 0.31 seconds ahead of her nearest rival Tessa Worley of France.
Italian Sofia Goggia was third. Shiffrin, who won her maiden overall World Cup title last season, tops the overall standings with 1,181 points, a huge lead of 647 points over second-placed Viktoria Rebensburg of Germany.
This season she has won three slalom races, two giant slaloms, one parallel slalom, the Oslo city event and a downhill.
'I’m trying to decide' - Shiffrin to make Winter Olympics decision
It was her third World Cup win in a row in all disciplines and her sixth in the last seven races, her form peaking with the Winter Olympics in Pyeongchang just one month away.
Shiffrin is widely expected to retain the Olympic slalom title she won at the 2014 Games in Sochi, Russia, as well as having a shot at gold medals in the giant slalom and Super G.
World Cup wrap: New era finally here after season where anything was possible
Robinson's sizzling run denies Shiffrin in final giant slalom of season