After finishing seventh in Saturday's first stage sprint of the Tour de Ski, Oestberg kicked off 2017 in style with victory on stage two, taking top spot with a time of 13:21.2 minutes.
It saw her finish seven seconds ahead of countrywoman Heidi Weng, with Finland's Krista Parmakoski completing the podium line-up.
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Switzerland's Nadine Fahndrich, known more for her sprint abilities, recorded her best-ever World Cup finish with a fourth place, and was joined by her team-mate Laurien van der Graaff in the top ten, another personal best for a Swiss sprinter in a distance event.
Ingvild Flugstad Oestberg
Image credit: Imago
Victory ensures Oestberg takes over the Tour lead by 10.3 seconds ahead of Weng, with Sweden's Stina Nilsson, who led after day one, occupying third place overall.
Oestberg said: "I wanted to prove to myself after yesterday that I could ski like I did today.
"I knew it was important to make it to the semi-final but I did not expect to not make it out of the semi-final. Such a result sometimes makes you give your best."
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