Ligety roared out of the first run with a .93-second lead that no one could catch. He posted a cumulative time of 2:45.29 to finish, .48 ahead of silver medalist Steve Missillier of France. Another Frenchman, Alexis Pinturault, won the bronze.
"This is the event I wanted the most," Ligety, 29, said after the victory. "This is the event I have been putting so much pressure on myself to win, so to pull through is an awesome feeling." Ligety is the first American man to win two Olympic gold medals in alpine skiing, joining American Andea Mead-Lawrence, who herself won gold in the slalom and giant slalom at the Olso Games in 1952.
"The plan was to really just nail a couple of big rolls," Ligety told reporters after the first run. "This hill is not difficult skiing wise, but it's difficult tactically. I was trying to be smart over those big tactical terrain changes, then push as hard as I could in the sections where I knew I could take some risks."
It paid off for the man who won three gold medals at last year's World Championships.
Ligety has been one of America's best skiers for eight years but has also been in the large shadow of stars Bode Miller and Lindsey Vonn.
His victory gives the U.S. team four medals with the men's and women's slalom races coming. Ligety and Mikaela Shiffrin are expected to be in the running for medals in both of those events.
Austrian Marcel Hirscher was one of many who believed in Ligety.
"He is just brilliant," said Hirscher, who finished fourth. "The best guy won today. Before the race started it would have been a big surprise if someone beat him."
San Jose native Tim Jitloff finished 15th with a time of 2:47.13, while Jared Goldberg of Salt Lake City was 19th. After winning a bronze medal last weekend, Miller was 20th.
Miller, 36, said he hurt his left knee during the super G, the race he got his sixth Olympic medal.
"Managing it has been the biggest challenge this year, coming back from injury," he told reporters. "Your body, when you go off snow for a while, doesn't like getting back into it.
"If you keep skiing every day, you get used to it."
Miller said he changed equipment because of a crash he had at St. Moritz, Switzerland, last month.
"I didn't feel like I could take another crash like that,' he said. "It's been maintaining some pretty good puffiness in there through this whole couple weeks."