The 22-year-old American blitzed the field in snowy and windy conditions, producing the best combined time over two runs of one minute, 40.91 seconds at the Killington Mountain ski resort in Vermont.
The win for Rebensburg came four weeks after she won the giant slalom in the first race of the World Cup season in Soelden, Austria.
"It wasn't easy but when I ski balanced, it makes it easier than when I don't".
With a cold north wind blowing, a number of athletes struggled in the second run with visibility and the slick, icy course.
Shiffrin will look to be the first skier to win back-to-back gold medals in slalom when she competes at the Winter Olympic Games in Pyeongchang, South Korea, in February. The win was the 26th World Cup slalom victory for Shiffrin, who is third all time. Austria's Bernadette Schild finished third in 1:43.58, a distant 2.67 seconds back.
In her last 21 World Cup slalom races, Shiffrin rose to the podium 20 times, with 16 wins, two second places, two thirds with only one DNF in the entire period. With a win and a second-place finish each, Shiffrin and Vlhova are now tied for the slalom points lead. "I wanted to have the same mentality as the first run: Be smart, but let it fly". "Petra had a great second run, so there are quite a few girls who want it just as much as I do and the difference comes with the skiing, comes with the discipline, and that's where I'm going to come out on top".
Shiffrin was the runner-up in Saturday's giant slalom and now leads the overall World Cup standings with 305 points.
"Winning the race proves that you are on the right track, so I'm very happy with my win today in Lake Louise", Jansrud, who started last season with three super-G wins in a row, said. "It was a sweet race today, it was really fun to ski". This year, though, she used her nervousness "It was more like fuel".
Austria's Hannes Reichelt was 0.32 seconds back in third. "But I also took a little bit of extra risk where I may have gained some time".
Kjetil Jansrud of Norway won the World Cup super-G on Sunday, beating Austrian's Max Franz by 0.28 seconds.