Shiffrin secured the overall Friday when Ilka Stuhec of Slovenia decided to skip the slalom. Shiffrin was drowsy when her mom came into her room and delivered the news.
"It didn't seem like a real thing, because it's odd to say I won something in ski racing when I wasn't actually out on the hill," said Shiffrin, who will receive her trophy Sunday. "It will feel more real tomorrow, definitely, when I'm actually holding it."
"It's been a goal and a dream of mine since I was 5 years old. It's really difficult to understand something that finally happens after 20 years," she said.
The 22-year-old Shiffrin becomes the fifth American ski racer to win the overall crown, joining Phil Mahre (1981-83), Tamara McKinney (1983), Bode Miller (2005, 2008) and Lindsey Vonn (2008-10, 2012).
McKinney couldn't be happier that Shiffrin joined such an elite club. She watches virtually every race on television, but caught this one in person.
"Mikaela's got the whole package, where she's worked hard, and loves what she does," McKinney said. "That's at the core of it. It's been really exciting to watch."
To think, Shiffrin's true goal this season was more modest: Win every single slalom race.
Well, modest for her anyway.
The Olympic slalom champion captured six slalom races this season, but was really hoping to win in front of a bipartisan crowd, which was boisterously cheering and waving signs.
Typically, it's Shiffrin who uncovers speed at the bottom of a course. Not this time, though, as Vlhova finished in a combined time of 1 minute, 32 seconds to eclipse Shiffrin by 0.24 seconds on the sun-drenched hill. Sweden's Frida Hansdotter was third.
"If you want to win, you have to ski without mistakes, perfect," explained Vlhova, who led Shiffrin by 0.07 seconds after the first run. "Today, I did. It's an amazing day for me."
After seeing her name in front, Vlhova dropped to the snow in the finish area and raised her skis toward the sky. Later, Vlhova was so teary-eyed over winning her first World Cup race since Dec. 13, 2015, that it touched Shiffrin.
"I know that feeling. It's so special when anybody feels that," Shiffrin said. "Everybody has a bad day on some races. It's so cool to see it when somebody has a good day."
When closest rival Lara Gut of Switzerland tore her ACL in February, the overall title appeared all but inevitable for Shiffrin. But Stuhec made things interesting down the stretch. Stuhec won the downhill at World Cup Finals and finished second in the super-G to keep the possibility afloat. She said Friday at the team event she was skipping the slalom because of fatigue.
Shiffrin captured 11 races this season, which also includes a city event, three giant slaloms and an Alpine combined. She boasts a 278-point lead over Stuhec with one race remaining.
In addition, Shiffrin locked up her fourth slalom title in five seasons before the race. On Sunday, she has an outside chance at a giant slalom crown, trailing Tessa Worley of France by 80 points.
Don't expect her to hold anything back, either.
"That's the whole point of ski racing, to always put you best skiing out there," Shiffrin said. "I hate it when people start races and say, 'I just wasn't feeling it today.' Or when people tell me, 'Why are you skiing so hard, you know you're going to win?'
"If you're going to race, you have to do your best. Sometimes, your best is better than other days. ... I wanted to close out the season strong."
Women's Slalom results
At Aspen, Colo.
(First-second runs in parentheses)
1. Petra Vlhova, Slovakia (45.52-46.48) 1:32.00.
2. Mikaela Shiffrin, United State (45.59-46.65) 1:32.24.
3. Frida Hansdotter, Sweden (45.55-46.80) 1:32.35.
4. Veronika Velez Zuzulova, Slovakia (45.66-46.73) 1:32.39.
5. Melanie Meillard, Switzerland (46.00-47.05) 1:33.05.
6. Wendy Holdener, Switzerland (46.33-47.08) 1:33.41.
7. Emelie Wikstroem, Sweden (46.44-47.50) 1:33.94.
8. Sarka Strachova, Czech Republic (46.51-47.46) 1:33.97.
9. Bernadette Schild, Austria (46.89-47.11) 1:34.00.
10. Marina Wallner, Germany (47.68-46.56) 1:34.24.
19. Resi Stiegler, United States (48.64-47.36), 1:36.00.
World Cup Slalom Standings
1. Mikaela Shiffrin, United States, 840 points.
3. Wendy Holdener, Switzerland, 520.
2. Veronika Velez Zuzulova, Slovakia, 485.
4. Frida Hansdotter, Sweden, 442.
5. Sarka Strachova, Czech Republic, 424.
6. Petra Vlhova, Slovakia, 411.
7. Bernadette Schild, Austria, 331.
8. Nina Loseth, Norway, 302.
9. Emelie Wikstroem, Sweden, 220.
10. Maren Skjoeld, Norway, 197.
18. Resi Stielger, United States, 132.
49. Megan McJames, United States, 11.
World Cup Overall Standings
1. Mikaela Shiffrin, United States, 1693.
2. Ilka Stuhec, Slovenia, 1,449.
3. Sofia Goggia, Italy, 1,263.
4. Lara Gut, Switzerland, 1,130.
5. Tessa Worley, France, 976.
6. Tina Weirather, Liechtenstein, 969.
7. Federica Brignone, Italy, 955.
8. Wendy Holdener, Switzerland, 862.
9. Viktoria Rebensburg, Germany, 734.
10. Petra Vlhova, Slovakia, 597.
13. Lindsey Vonn, United States, 528.
23. Laurenne Ross, United States, 422.
43. Jacqueline Wiles, United States, 198.
50. Stacey Cook, United States, 163.
51. Breezy Johnson, United States, 162.
59. Resi Stielger, United States, 135.
81. Alice McKennis, United States, 51.
103. Megan McJames, United States, 21.
130. Anna Marno, United States, 3.