Eckhoff came home in 34:23.1 minutes with one penalty to claim her second victory of the season, with Gabriela Koukalova of the Czech Republic the runner up 22.6 seconds further back.
Despite finishing second-best in Oslo Koukalova could still celebrate securing the small crystal globe for the mass start.
Laura Dahlmeier of Germany started the day with an 11-point lead over Koukalova in the mass start standings, but that lead disappeared when the German finished ninth, with three penalties.
And completing the podium in Oslo was Kaisa Makarainen of Final, who moved from sizxth at the start of the last loop to finish 34.5 seconds behind Eckhoff.
Despite her ninth-place finish Dahlmeier finished top of the overall World Cup standings on 1211 points, with Koukalova second with 1089 and Makarainen third with 971.
Read the original article on Eurosport: Eckhoff wins finale in Oslo