Loudly cheered by 14,800 spectators, Hansdotter built on her first-run lead to finish in a combined time of 1 minute, 49.59 seconds.
Tina Maze of Slovenia was 0.61 behind in second, and Olympic champion Mikaela Shiffrin of the United States improved from a disappointing opening run to finish third, 0.63 behind.
"I don't feel like a favourite but for sure it's fun if I would be a favourite," Hansdotter said about the Feb. 14 world championship race in Beaver Creek, Colorado — where Shiffrin will be defending her title.
"I just need to ski my skiing and ski good and then the results are coming," she said. "You can't be focusing on where you should end up. You just need to focus on what you should do with your skis."
Hansdotter led Maze by 0.23 after the opening run but used a flawless final run for a convincing win.
It was the Swede's 14th career World Cup podium but only second victory. She also won in Kranjska Gora, Slovenia, last season.
Hansdotter now has 420 points in the slalom standings, with two-time champion Shiffrin in second place on 379 points.
"Good training, hard training, and know what you need to do," Hansdotter said about her consistency this season. "In training, I always try to be on the limit, but not over the limit. That is the hard part, to really be on your top but don't ski more than you can."
Erin Mielzynski of Collingwood, Ont., was 12th.
Maze went further ahead in the overall standings with 857 points, well ahead of Shiffrin on 605 points. However, Maze has two weekends of speed racing coming up in Cortina d'Ampezzo, Italy, and St. Moritz, Switzerland, while Shiffrin won't race on the World Cup until after the world championships.
"I was really easy today," said the Slovenian, who looks set for a repeat of her 2013 overall triumph. "I was training good the last days and I was pretty confident about my slalom here."
Maze benefited from the cancellation of a downhill and a super-G in Austria last weekend.
"We were training slalom in Bad Kleinkirchheim so you get more slalom turns in your legs and in your head," Maze said. "The schedule is crazy doing all the events. It takes a lot of energy and adaption to each discipline."
Shiffrin, who had won the event for the past two years, avoided mistakes in her first run but was still 0.68 behind Hansdotter in eighth.
The American looked more aggressive in her second run and posted the second-fastest time after Veronika Velez-Zuzulova of Slovakia.
"I felt like the surface was better the second run," Shiffrin said. "I was able to get an edge in the snow and I found some response and I was able to arch cleaner turns."
Despite posting the fastest time up to then, Shiffrin shrugged after crossing the finish line.
"I didn't think my second run was good enough or fast enough to win today because Tina and Frida are so strong."
After winning in Kuehtai, Austria, and Zagreb, Croatia, recently, Shiffrin missed out on yet another record — as no Americam skier has won three World Cup slaloms in a row.
Eight of the 30 skiers who qualified for the second run failed to finish on the demanding course.
The annual night slalom is the race with the highest prize money on the women's circuit, with the winner taking home nearly 53,000 euros ($62,300).
"So now I don't need to ski anymore?" Hansdotter joked about her paycheque. "That's not the things I am thinking about when I am racing. But for sure it's good for the future."