Seconds later, crouched low over skis, Shiffrin sailed over the finish line to become, at 18, the youngest slalom winner in Olympic history.
Ironically, her hair-raising victory came at the expense of her skiing idol, Austria's Marlies Schild, whose 35 World Cup slalom wins are the most in history.
Schild, 32, took the silver medal and her countrywoman, Kathrin Zettel, the bronze in the final women's Alpine event of these 2014 Winter Olympics.
"I didn't lose the gold medal," said Schild. "I won silver in the second run. My dream died in the first run down."
With her win at the Rosa Khutor Alpine Center course, the precocious Shiffrin put herself in position to come to the 2018 Games in South Korea as one of the American ski team's best-known names.
The Coloradan, who became the youngest skier to win a World Championship in 2013 and led the World Cup standings in the event this season, lost time in the near fall. But the 0.49-second lead she had on the field after the morning run gave her plenty of cushion.
Her combined time of 1 minute, 44.54 seconds was 0.53 seconds ahead of Schild's, 0.81 in front of Zettel.
"That [the near fall] was a pretty crazy moment there," said Shiffrin. "I was like, 'I'm not going to make it. I'm not going to make it.' I threw on a hockey stop right there. That was a little bit tough. It scared me half to death."
By winning her pet event, Shiffrin also became the first American gold medal-winner in the slalom since Barbara Cochran in 1972.
Before the race, the extremely confident teenager had counseled her coach not to worry.
"I'm going to win this thing," she told Pfeifer. "I'm going to do the same thing Ted Ligety [the giant slalom gold medalist] did. I'm the world champion and I'm going to do it."
She was true to her word in the morning run, her time of 52.62 providing her with a sizable lead over her most dangerous competition.
Skiing just before the winner on a rare cold night in the Caucasus, veterans Maria Hoefl-Reisch and Tina Maze couldn't get it going during their final run.
Shiffrin had a lead of 1.34 seconds on Schild when, to the sound of clanging cowbells, horns, and screams, she jumped out of the chute-like gate on her second run.
Rocking back and forth rhythmically, as if she were engaged in a twist contest, Shiffrin looked in full-control early.
"I felt like I was really charging out of the start and had a good speed going," she said. "That always makes me feel more comfortable on my feet. I thought the most fun part of the course was coming up, five gates really tight. You're basically wiggling your feet back and forth. It's really fun."
That reverie was interrupted midway down when she caught the edge and her leg shot up.
"It was a crazy moment," she said.
Before that run, her mother, an ex-ski racer, had told her to relax.
"I told her, 'You don't have to be 100 percent, but don't make any big mistakes,' " said Ellen Shiffrin. "Fortunately, she regrouped so well."
In the typically chaotic aftermath of an Olympic event, Shiffrin appeared calmer than her mother, her coach, and virtually everyone else.
"This is why we're all here, isn't it?" she said. "I wish I could have an American flag on my back at every World Cup race because that's an amazing feeling to know you're representing not just yourself or your team or your family but your entire country."