A day after securing record victory No. 83, Shiffrin added her 84th win Wednesday in another giant slalom on the same course.
And as she did a day earlier, Shiffrin led from start to finish, dominating the first run down the steep Erta course and then adding to her advantage in the second run.
Shiffrin finished a massive 0.82 seconds ahead of two-time Olympic silver medalist Ragnhild Mowinckel and 1.19 ahead of Olympic champion Sara Hector.
When Shiffrin reached the finish after her second run, she collapsed to the snow in apparent exhaustion -- with her skis still attached to her boots -- before Mowinckel and Hector came over to congratulate her and helped her up.
"Oh my gosh," Shiffrin said. "I was pushing so hard, and I just hoped I ended up on the right side of all the gates. Now I'm a bit dead mentally -- just so tired. But when you ski like that, it keeps your energy going, so, just an incredible feeling."
Tuesday's win moved Shiffrin ahead of the previous women's mark of 82 victories held by former American teammate Lindsey Vonn, and Wednesday's victory moved her within two of the overall record -- in men's or women's events -- of 86 wins held by Ingemar Stenmark.
Vonn retired four years ago when injuries cut her career short, and Stenmark raced in the 1970s and 80s.
If Shiffrin wins two slaloms in Spindleruv Mlyn, Czech Republic, this weekend, she could match Stenmark on Sunday.
"Technically, it is possible," Shiffrin said with a laugh. "We'll see if I can put the energy on my slalom skis for two more races.
"It's been busy, and I am in a kind of an unfortunate time of my monthly cycle, so I'm more tired right now. We just normalized talking about that," she added.
Spindleruv was where Shiffrin made her World Cup debut as a 15-year-old prodigy nearly 12 years ago.
"It's a special place for me," she said. "So I'm really looking forward to go."
Former World Cup giant slalom champion Marta Bassino was on track for the podium before she lost control a few gates from the finish and plowed through a gate, which hit her hard in the shins.
It was Shiffrin's 10th win of the season and her 19th career victory in giant slalom, moving her within one of Vreni Schneider's record of 20 in the discipline.
Shiffrin said she had a late night after her record-breaking day.
"But it was a really nice evening," she said. "It was so nice to see messages from people and so much support and so much excitement about the race. I was definitely looking a lot at all of that and then trying to go to bed and have a good night's sleep. And I was awake at midnight. I was awake at 3. Then I was awake at 5. I was hungry all night. I was like, 'Oh my gosh, I'm a mess.'"
Still, Shiffrin managed to pull herself together to bring out her best skiing again.
"After [Tuesday], I was just so tired, which made today pretty hard," she said. "And I felt nervous because when I am skiing tired, I make mistakes. And I didn't want to make a mistake today.
"In the first run, I thought, 'Either I am going out at the fourth gate or it's going to be a really good run.' It ended up being a really good run. The second run, I was just trying to trust my skiing and keep pushing, no matter what I felt."