The 32-year-old was forced to miss the whole of the Tour de Ski and the last World Cup in the Czech Republic having been hospitalised before Christmas with a heart problem.
Bjoergen had been expected to return for the sprint in Liberec but didn't, although any doubts that she would be affected by the situation were put to bed in France.
For the triple Olympic champion was back to her best in the 10km classic mass start, beating World Cup leader Justyna Kowalczyk in particular by 18 seconds on the way to victory.
Bjoergen clocked a winning time of 27:04.6minutes with Therese Johaug, second in the overall World Cup standings, by 2.7seconds before Kowalczyk back in third.
That maintains Bjoergen's unbeaten World Cup record this season, having won the opener in Gaellivare and then all three stages of the Ruka Triple before skipping the four races in Canada.
She now sits seventh in the World Cup rankings with 562 points with four-time Tour de Ski winner and leader Kowalczyk now up to 1372 and Johaug second with 947.
- Sports & Recreation