Mild and rainy weather forced organizers to shorten the course and change the format of the competition.
But it didn't stop Harvey, in fact nothing looked like it would as he carried on despite his right ski breaking early in the race and needing to be replaced.
With fog also coming down on the course, Harvey covered the distance in 9:03.4 minutes to edge compatriot Kershaw by 4.1 seconds, while Chris Jespersen of Norway was third, 10.2 seconds behind.
In the women's prologue overall cross country World Cup leader Marit Bjoergen led a one-two Norwegian finish in a 3km race.
Bjoergen came home in 6:34.4 minutes to leave teammate Astrid Uhrenholdt Jacobsen 1.9 seconds behind in second, with Sylwia Jaskowiec of Poland third.