Bjoergen, unbeaten in this event this season, came home in 24:23.6 minutes to claim her sixth win of the World Cup season.
That was enough to pip overall World Cup winner Weng, who was 0.6 seconds further back.
There was almost an all Norwegian podium but Ingvild Flugstad Oestberg's time of 24:31.4 was only good enough for fourth.
That was because Krista Parmakoski of Finland crossed in 24:26.5 to claim the final step on the podium.
The result sees Weng move onto 1826 points, while Parmakoski is second on 1498 and Oestberg is third with 1422. Victories sees Bjoergen sit fifth overall on 1057 points, with fourth-placed Stina Nilsson of Sweden, who was 16th in Quebec City, on 1274.
Read the original article on Eurosport: No beating Bjoergen in 10km mass start