Seven years after winning the discipline's Olympic crown in Sestriere, Ligety proved he was more versatile than ever, clinching victory in a combined time of two minutes 56.96 seconds.
Ligety, who won the super-G last week, will also be the hot favourite in the defence of his giant slalom crown on Friday as he bids for a formidable hat-trick.
His performance was all the more spectacular as he had never won either a super-G or a super-combined in the World Cup before the world championships and the 28-year-old from Salt Lake City could even be a threat in Sunday's slalom.
On the steep and icy slalom course at the bottom of the Planai piste, home of a famous floodlit slalom on the World Cup circuit, Ligety adopted a dangerous strategy.
"I took all the risks after my great downhill run. I knew I had a chance but I was looking to ski smart also, it was easy to ski out as the run was so tough," he told reporters.
"I have huge routine being on the tour for nine years, so I can handle pressure well and these worlds have been pretty exciting for me so far," he added.
He promised more excitement in the week ahead.
"My slalom has not been so satisfying in recent seasons but this performance will encourage me to keep fighting hard to improve my level in that specialty too," Ligety said.
"Now I'm looking forward to another great race in the GS. There will only be one possible tactics then - charge as hard as possible."
Ivica Kostelic was the favourite after winning Kitzbuehel's classic combined for the fourth time shortly before the worlds, but the Croatian played it too safe in the slalom run.
"I didn't find a good rhythm today and I had a bad feeling going through that run. It was bad skiing," he said after finishing second, 1.15 seconds behind the American.
"I did not deserved to be on the podium after such a bad slalom run following that great downhill leg," he added.
Romed Baumann cheered the Austrian camp by snatching the bronze, 0.02 seconds behind Kostelic, only the host country's second medal after six events.
"There was lots of pressure on me this evening and I needed some time to really ski the aggressive skiing I was hoping for," he said.
"I felt that I needed to push harder in the lower part - especially after hearing the speaker and the crowd pushing me. This bronze medal of course means a lot to me and also to my team."
Downhill world champion and title-holder Aksel Lund Svindal of Norway straddled a gate halfway down after looking on course for a podium spot.
French favourite Alexis Pinturault skied by far the fastest slalom run but a disastrous downhill leg left him sixth in the final standings.
- Sports & Recreation