And Johaug, who now leads the overall World Cup standings by a considerable 587 points, could not hide her relief as she picked up her 15th individual race triumph of the campaign.
"I heard when I was maybe six kilometres from the finish that I had a 40-second lead and I didn't really understand what I was doing," she said.
"But Ingvild was really strong behind me and she had a really good finish, and when I heard that she was just five seconds behind me I had to fight with myself.
"But I'm just so happy that I could be the first on the podium today."
Weng now lies second in the overall table on 1,303 points, while Russia's Natalia Nepryaeva is third despite not taking part in Thursday's event.
But it was the 31-year-old Johaug who continued her stunning season as she held off Oestberg's late charge to seal the 70th individual World Cup win of her career.
Alexander Bolshunov was another skier who consolidated his advantage at the top of the standings, beating Johannes Hoesflot Klaebo and Emil Iversen to pick up his seventh race victory of the season.
The Russian – who has a healthy 486-point-lead at the summit of the table – finished with a time of 1hr19m34.9s in Norway, holding off Klaebo by 51.7s to bounce back from his second-place finish in Ostersund on Sunday.
Klaebo's performance now leaves him on 1,324 points in the standings, while Sjur Roethe – who could only muster seventh in Meraker – is third on 1,024.
The cross-country World Cup stays in Norway and now heads to Trondheim on Saturday, where Johaug and Bolshunov will seek to continue building their imperious advantages at the top of the table.