The Austrian star extended his first-run lead to finish 0.93 ahead of Henrik Kristoffersen of Norway in a familiar runner-up spot. Andre Myhrer of Sweden was third, 1.72 back.
Hirscher's domination was so complete he also had the fastest time in the second run, 0.34 quicker than Kristoffersen, by attacking his rival's target rather than protecting his lead.
"I have been on the limits, especially on the steep part, so everybody is beatable," Hirscher said.
Hirscher's fifth straight success in slalom was the 53rd World Cup win of his career yet a first at the storied Swiss course where he is a three-time runner-up.
"It's something big for me. This was the last classic race on the calendar that I haven't won until today," the reigning slalom world champion said.
Earning 100 World Cup points, Hirscher stretched his lead over second-placed Kristoffersen in both the overall and slalom season-long standings. Hirscher is the six-time defending overall champion.
Yet again at a post-race news conference, Kristoffersen was asked how it is possible to beat Hirscher on current form.
"He is just better, that's the way it is," said the 24-year-old Norwegian, who has seven runner-up finishes this season without a win. "I will never give up, that's for sure."
Hirscher is third on the men's all-time World Cup wins list and will be favored to match the 54-win total of Austrian great Hermann Maier next weekend. Appropriately, the World Cup circuit now moves to celebrated Austrian venue Kitzbuehel.
At age 28, Hirscher would need several more years of consistent winning to catch the 86 wins of Ingemar Stenmark, the Swedish great who raced slalom and giant slalom in the 1970s and 80s.
Stenmark won Olympic gold medals in both technical races at the 1980 Lake Placid Olympics, and Hirscher shapes as favorite to repeat the feat next month in Pyeongchang, South Korea.
In the 2014 Sochi Olympic slalom, Hirscher and Kristoffersen took silver and bronze, respectively, behind the now-retired Mario Matt of Austria.
"Right now, Marcel is in a league of his own," said Myhrer, the 2010 Olympic bronze medalist.
In a World Cup comeback after three years out injured, Nolan Kasper of the United States placed 20th.
The 28-year-old Kasper's return could be in time to earn a third Olympic selection. He placed 13th and 24th in the previous two Olympic slaloms.
Kasper was joined in the top 20 Sunday by another racer wearing a starting bib number in the 50s. Ryunosuke Ohkoshi of Japan was 19th, 4.94 behind the winner.
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