The slopes at the Lapland ski resort were perfect for Vlhova, who won the race 1.41 seconds ahead of Lena Duerr from Germany with a total time of one minute 50.59 seconds.
"I am quite surprised but of course, I am happy because both runs were perfect from my side," Vlhova said.
"Sixth victory here in Levi, what to say? Honestly, I didn't expect so much of a gap between me and Lena and Katharina but I feel good. I am enjoying skiing and I feel confident too."
Vlhova took the lead in the first run and extended it in the second, finding her rhythm from the gates and building momentum as she descended.
Austria's Katharina Liensberger came third, 1.55 seconds behind Vlhova.
"It was amazing to show this performance today into the new season, it's really a new beginning for me," Liensberger said.
"I just wanted to ski fast for myself and it turned out really good... I had a lot of fun today."
Shiffrin, who recently had a practice run tumble, couldn't maintain the pace in the course's final stretch and ultimately trailed Vlhova by 1.70 seconds.
The men's downhill race in Zermatt-Cervinia, on the border between Switzerland and Italy, was cancelled earlier on Saturday due to heavy snowfall and winds.
