The 24-year-old Norwegian claimed the World Championship title in the 10km freestyle in Val di Fiemme last month and dominated over triple the distance on home snow.
Johaug increased her lead at the front from 0.4seconds after 1.8km to 15.1 by the 8km mark, a gap that was not to be breached as the Norwegian powered her way to victory.
Her lead was up to over a minute and a half as the 25km mark approached however she relaxed with the win assured over the final kilometres, even taking a Norwegian flag with 500 metres to go.
Johaug clocked a winning time of 1:21:17.7hours with her eventual margin over World Cup champion Justyna Kowalczyk 46.6seconds with Yulia Tchekaleva third 5.3seconds back.
Kowalczyk took the overall World Cup title with victory in the classic sprint in Drammen on Wednesday, aided by the fact that Johaug, the only one who could catch her, opted out.
The race for the distance World Cup title could go the same way with Kowalczyk still with a healthy lead at the top although Johaug's victory in the 30km freestyle mass start did cut it to 146 points.