It followed the dominant Austrian's giant slalom win of the day before and was his eighth of the season.
He relegated Henrik Kristoffersen to second place, but the Norwegian sealed the discipline's crystal globe.
Hirscher has extended his lead in the overall standings to 353 points over Kristoffersen with only six races remaining of the 2016 season.
Italian Stefano Gross completed the podium in the slalom.
"It's incredible, it's my first crystal globe!" said 21-year-old Kristoffersen, who signaled Saturday that he would not attempt to compete in the speed events such as downhill or super-G which make up the bulk of the remainder of the season.
But it's been a remarkably consistent season for the rising star, with 12 podium spots.
"Henrik has assured us that he won't take part in the super-G, but maybe that was a joke," Hirscher said Saturday after wrapping up his giant slalom win from Alexis Pinturault of France and Kristoffersen.
"It is obviously a very special day for me," Hirscher added. "Looking at my statistics, this has been my best year. But is has also been the season where I have had to fight the hardest."
"(The day's) first run was maybe the most difficult run I have ever skied in eight years of World Cup giant slalom. It was so bumpy and rough," Hirscher said.
Saturday's win also ensured Hirscher would take his 17th podium place this season and snap up the World Cup giant slalom crystal globe for the second year in a row.
He leads Pinturault by 111 points with only one giant slalom event remaining in St Moritz later this month.