The resounding wins are the first time Australian athletes have won both the men's and women's events in the one discipline at World Cup level.
The double victory at Bardonecchia was the penultimate round of this year's World Cup series as Australia's halfpipe team is celebrating their best ever international season.
Johnstone's win at the halfpipe site of the 2006 Winter Olympic Games has shot the 21-year-old to the top position of the World Cup halfpipe standings and also given him leadership of the overall snowboard freestyle points table ahead of Japan's Ryo Anono.
Fellow Australian Institute of Sport and NSW Institute of Sport scholarship holder, Holly Crawford, is also enjoying a strong position in second place on the points table and is now applying pressure to China's competition leading rider Xuetong Cai heading into the last event.
With the men's and women's winners of the next round chasing 1000 points, Crawford and Johnstone have transformed the season-ending event in Arosa, Switzerland, on March 26, into a winner-take-all shoot out between the Australians and their Japanese and Chinese rivals.
Johnstone said last night after easily accounting for French duo Johann Baisamy and Arthur Longo, who finished second and third, that he is looking forward to competing in Arosa.
"I'm pretty happy," Johnstone said after the win. "I really wanted to get a win here to get me back in a good position in the points ranking.
"Now, I guess, we could have a good show in Arosa."
Crawford was victorious over France's Mirabelle Thovex, who enjoyed her first World Cup podium, while Polish rider Paulinas Ligocka-Andrzejewska was third.
Halfpipe head coach Ben Alexander said he was ecstatic about the double victory.
"To see Holly and Nate standing on top of the podium was an incredible sight," Alexander said.