The Norwegian, a member of the team which won the gold medal at the Sochi 2014 Winter Olympic Games, completed the course in 37min 44.4sec.

Her time was enough to see her edge team-mate and current World Cup leader Heidi Weng, who crossed the line 7.9 seconds slower.

Krista Parmakoski of Finland rounded off the podium as she took third place, a further 8.8 seconds back.

Østberg remains 70 points adrift of Weng, the Olympic bronze medallist in the 15km skiathlon, on the overall standings as she has 469.

Weng leads the way with an impressive total of 539, while Parmakoski’s bronze maintains her excellent start to the 2016-2017 campaign.

“There has been a lot of training for several years to win today,” Østberg said.

“This is my first victory in a race longer than 10 km.

“I am surprised and happy.

“My plan was to start little bit slow.

“I knew Krista and Heidi would speed up so I needed to keep my pace.

“Davos has been great for me. I had my first sprint World Cup win and now the longest win.”

In the men’s race, held over 30km, Norway’s Martin Johnsrud Sundby maintained his excellent opening to the season as he extended his advantage on the overall leaderboard with another win.

The 32-year-old, a silver medallist at Vancouver 2010 and bronze medallist at Sochi 2014, demonstrated his prowess over the longer distances once again as he crossed the line in 1hr 7min 31.6sec.

Relay world champion Anders Gløersen, also of Norway, clocked 1:07:45.3 to clinch silver, while Finland’s Matti Heikkinen was a further 12 seconds adrift.

Sundby now heads the overall standings by 134 points on 450, with Sweden’s Calle Halfvarsson his closest challenger.

The event in Davos continues tomorrow.