Hirscher's time for his two runs totaled 1 minute, 44.34 seconds and gave him his first career victory at Kitzbuehel.
Felix Neureuther of Germany was a distant second at 1:45.11 followed by Croatian veteran Ivica Kostelic.
"I tried my best, but it was pretty difficult," Hirscher said. "I knew that Felix had an awesome (first) run and that I would need to give it my best to win the race."
Hirscher extended his lead over Norway's Aksel Lund Svindal in the overall points race to 1,035-921. Svindal did not compete Sunday. Hirscher also leads second-place Neureuther in the slalom standings.
The high-flying Hirscher's lack of a win at the legendary Kitzbuehel was a major media focus during the week, but he said he did not let it get to him. "I always try to just focus on my skiing," he said.
David Chodounsky was the top U.S. finisher in 21st place.