Ligety, the best giant slalom specialist on the Alpine ski circuit and ready to defend his world crown in the shorter discipline next week, made the best of a course suiting his technical skills to win in one minute 23.96 seconds.
It was the American's third major title after the combined Olympic gold in Sestriere in 2006 and the giant slalom world gold in Garmisch-Partenkirchen two years ago.
"It's wonderful. I can't believe it. It was a tough race, slippery with tough turns but I kept fighting. I think my love for free skiing must have helped me today in those difficult conditions," said Ligety, whose only World Cup podium in a super-G was second place in Val d'Isere three years ago.
"Last year I was not so lucky here, losing the giant slalom globe in the last race, but this is for sure a sweet moment. It means a lot to me and to the U.S. team after the hard crash of Lindsey Vonn yesterday," he added.
Olympic champion Vonn broke her shin and tore knee ligaments in a tumble during the women's super-G on Tuesday and will miss the rest of the season.
The technical nature of the men's course on the Planai piste also favoured unheralded Frenchman Gauthier De Tessieres, who took silver despite entering the competition as a reserve.
The 31-year-old from Clermont-Ferrand, also a giant slalom specialist, came on to the start list after team mate Johan Clarey was forced out with a back injury two days before the start of the championships.
De Tessieres, who had only one World Cup podium place behind him, finished 0.20 seconds behind Ligety for the highlight of a career plagued by injuries.
"Five days ago, I was down in the dumps at home. Unfortunately, Johan got injured. It's an odd feeling. But I really meant to do well, I was eager," he said.
"It was just great. I had a good feeling and the course suited me well."
Olympic champion and arch-favourite Aksel Lund Svindal had to be content with the bronze, 0.02 behind the Frenchman, for his ninth medal in a major event.
It was the worst result in the speciality this winter for the Norwegian, who has won three of the four World Cup super-Gs held since November and finished second in the other.
Svindal was probably disadvantaged by his starting position with the number 22 bib, as the earlier starters had better snow conditions.
"The snow was soft and rutted from all the runs ahead of me but it's part of the rules of our sport and you have to accept that, even though I enter every one of my races with victory in mind," said the Norwegian, who achieved the same result as his American girlfriend Julia Mancuso in Tuesday's women's super-G.
The first practice for Sunday's women's downhill took place without Vonn, who had been the clear favourite coming into the championships. She is due to undergo surgery on her return home to Vail.
Thursday is a training day in Schladming and the women's super-combined event is scheduled for Friday.
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