Hirscher was in third place after the first run and finished 0.76 seconds ahead of Thomas Farina of France with a two-run time of 2 minutes, 17.21 seconds.
Stefan Luitz of Germany finished third and Frenchman Alexis Pinterault took fourth.
Hirscher turned in a sparkling time on the second run of 1:08.29 on the icy hill. "This year they prepared it with more water than usual so you cannot imagine how hard it is to ski," said Hirscher. "It's a fight from top to bottom."
Despite the ice, the course was well suited to Hirscher's technical skills. "It is the steepest course on the tour and that suits me well," he said.
Hirscher's victory moved him into second place in the overall World Cup standings with 335 points. Aksel Lund Svindal of Norway led with 360 points after failing to finish Saturday's first run.