The 18-year old moguls skier from Montreal raced with a swollen blue bruise above her right eye, which was the result of kneeing herself in the face during training the previous day at Canada Olympic Park.
"That looks really bad, but I don't feel any pain," a jubilant Dufour-Lapointe said. "It's just a jackpot having a gold medal today."
Older sister Chloe, 21, finished second, marking the first time the Dufour-Lapointe sisters were one-two in a World Cup event.
Justine Dufour-Lapointe moved ahead of Heather McPhie of the U.S., who didn't advance from the opening qualifying round, into first in the overall women's moguls standings.
"It's amazing. I've never had this bib on," Dufour-Lapointe said, pointing to the season-leader's yellow bib. "It's incredible.
"I've never dreamed about that and now it's happened."
Mikael Kingsbury of Deux-Montagnes, Que., continued his domination of men's moguls. His gold Saturday was his 18th consecutive World Cup medal, which extends the previous record of 13.
The defending World Cup moguls champion is threatening to run away with this year's title too with a second straight victory following a win in Lake Placid, N.Y., last week.
But the 20-year-old found himself in an unfamiliar position in Calgary. Kingsbury was fifth in the last round of qualifying before the finale, which features the top six men racing for medals.
"I think that made me have a knife in my teeth — I don't know if that's an expression in English," Kingsbury said. "Going up to the last run I said 'OK, it's my first time in a super final that I'm low like that, so I'm just going to push and make the other guy push behind me.'"
Reigning Olympic champion Alexander Bilodeau made a mistake in the middle section of the course between the two jumps, which was an area that claimed several skiers Saturday.
The Rosemere, Que., native finished fifth and ranks second behind teammate Kingsbury in the moguls standings.
Bilodeau, 25, took most of last season off from competing. He will attempt to defend his Olympic gold in Sochi, Russia, next year before retiring.
"I skied quite well, but did a mistake on the middle section," Bilodeau said. "A lot of people made mistakes and I couldn't manage my way down."
Eliza Outtrim of the U.S. was third behind the Dufour-Lapointe siblings.
Olympic women's champion Hannah Kearney qualified first for the medal races, but the American also faltered on the course's mid-section while the Dufour-Lapointe sisters watched from below.
"For sure, I was surprised because she's really consistent," said Chloe Dufour-Lapointe. "She's a good skier. Today wasn't her day."
Alexandr Smyshlyaev of Russia was second behind Kingsbury. His second air element, called a "truck driver", is a crowd pleaser because it's a sideways flip in a pike position while he grabs the bottom of his skis with his hands. Sho Endo of Japan finished third.
Calgary was the lone Canadian stop on the World Cup moguls circuit this season. Kingsbury and the Dufour-Lapointe sisters each received a $5,000 bonus in memory of Canadian freestyle skier Sarah Burke, who died just over a year ago following a training accident.
WinSport, which oversees Canada Olympic Park, established the bonus last year for any Canadian finishing on the podium in a World Cup event at the sports venue. Kingsbury's win in Calgary was his third in as many years.
"It's a hard course and I think the great skiers can step up from the other ones," Kingsbury said. "It's not my home, but I feel like I'm at home. I'm super-stoked every time I come here."
Calgary is the second of five events this 2012-13 season in which the moguls skiers can earn results for early qualification to the 2014 Olympic team.
Lake Placid was the first with next week's World Cup in Deer Valley, Utah, the Olympic test event next month in Sochi and the world championship in Voss, Norway, the other races designated by the Canadian Freestyle Ski Association as Olympic qualifiers.
Two podiums plus a top-16 finish, with one of those results either from the test event in Sochi or the world championship, is enough for the skiers to know before the summer that they'll be a 2014 Olympian. Kingsbury has a head start on punching his ticket to Sochi.