Stassel, who finished 14th at the 2014 Sochi Winter Olympic Games, led the competition after the first two rounds and then managed an unbeatable score of 97.50 to beat Finnish defending champion Roope Tonteri, while fellow American Ryan Mack finished third.

"I was pretty nervous on top but once you drop in it turns into excitement and you just ride, I'm speechless," Stassel said.

"I have been working on that run for a long time and it feels really good to finally pull it all together here at the World Championships."

In the women's event, Onitsuka endured a tough time in the qualifying rounds but she pulled it together when it mattered, scoring 92.50 in the second round of the final to finish ahead of Anna Gasser of Austria, and Slovakia's Klaudia Medlova earned the bronze medal.

"I'm very happy, especially as the other girls were riding pretty good," Onitsuka said.

"I was very nervous, and I am proud to take home the gold."

Miyabi Onitsuka was also a shock winner as she took gold in the women's event ©Getty Images



In the freestyle skiing event, there was more success for the younger generation as 17-year-old Fabian Boesch became the first-ever Swiss men's world champion.

Boesch finished 23rd in Sochi but demonstrated his resilience and character by posting a score of 92.60 points despite a heavy fall in his first round.

The Swiss superstar was already assured of victory after a near flawless second round and skied the final run with his nation's flag in his left hand.

Australian Russell Henshaw fell just 0.80 shy of the gold medal while Noah Wallace completed an excellent day for the Americans by taking bronze.

Meanwhile in the women's competition, gold went to Lisa Zimmermann who amassed 85.80 points.

Lisa Zimmermann proved too strong for the rest of the field as she claimed gold in the freestyle ski slopestyle event ©Getty Images



"I am super happy," she said.

"But I know I can do these tricks a little bit better, so I am glad it was good enough, I've definitely had better runs."

Britain's Katie Summerhayes enjoyed a moment of history as she became the first British woman to win a Freestyle World Championships medal, completing what as a memorable day of action in Kreischberg.

Contact the writer of this story at [email protected]


Related stories
January 2015: Moguls stars Kearney and Kingsbury upgrade from silver to gold at World Championships
January 2015: Justine Dufour-Lapointe wins Freestyle Skiing World Championship moguls gold
January 2015: James and Cai claim halfpipe snowboard World Championship titles
January 2015: Jacobellis and Matteotti claim snowboard cross World Championship titles
January 2015: Qi and Peel secure aerials titles as Freestyle Ski and Snowboard World Championships opens