Hirscher trailed Felix Neureuther of Germany by 0.01 seconds after the first runs, but put in a storming second run to win in 1:49.79 minutes.
That meant that Neureuther had to settle for second as he crossed the line 0.53 seconds slower than Hirscher.
And the final step of the podium went to Mathieu Faivre of France in 1:50.98.
Hirscher had already clinched the season-long giant slalom World Cup title along with his sixth straight overall crown.
But that didn't stop him from claiming his fourth World Cup win in giant slalom this season, with the Austrian and Alexis Pinturault having won seven of eight races this season.
Pinturault had a fast second run going before hitting his left hip on the snow and skiing off course.
Read the original article on Eurosport: Hirscher brings up the hat-trick