Johaug swept aside the rest of the field, beating fellow Norwegian Ingvild Flugstad Oestberg by 15.5 seconds to extend her lead at the top of the World Cup standings.
While Johaug cruised home, there was just two hundredths of a second separating second and fourth place.
Oestberg edged Austria's Teresa Stadlober to make it a Norwegian one-two with Sweden's Ebba Anderson agonisingly missing out on a podium spot.
Meanwhile, Russia's Alexander Bolshunov continued his fine form with victory in the men's skiathlon.
He won by nine hundredths of a second with a strong Norwegian contingent taking the next four places.
Simen Hegstad Krueger was Bolshunov's closest challenger with Sjur Roethe beating fellow countrymen Martin Johnsrud Sundby and Hans Christer Holund into third place.