Under stunning blue skies at the Laura cross-country ski centre, Bjoergen won the second gold up for grabs anywhere at Sochi 2014 with a vintage display of the killer supremacy that strikes fears into her opponents.
Sweden's Charlotte Kalla screamed with delight as she crossed the line to take silver. Heidi Weng of Norway took the bronze, her first ever Olympic medal.
Bjørgen, 33, now has a total of four Olympic golds after winning three golds at the Vancouver Games in 2010 and has confirmed her status as one of the greatest cross-country skiiers ever.
Her fourth gold means she has now overtaken the legendary Norwegian figure skater Sonja Henie -- who won three golds from 1928-1936 -- in Norway's all time list for female Olympians.
She also became the oldest individual female Olympic Winter Games gold medallist in this sport.
Bjørgen, at 33 years and 324 days, took the record from Italian Stefania Belmondo who was 33 years and 27 days when she won the 15 km freestyle at Salt Lake City 2002.
'I can now relax a little'
Bjørgen, who said previously her aim was to win one gold medal in Sochi, commented that her her early success would allow her to enjoy the Games.
"One gold was my goal, so now I can relax a little bit. I can enjoy the rest of the Games," she said.
Kalla, who picked up a gold and a silver in Vancouver, was delighted over her second place. "This is my dream," she said.
The skiathlon is a combination of 7.5 km classic style immediately followed by 7.5 km freestyle skating, with the competitors rapidly changing skis for the different styles in a changeover area during the race.
The medallists, along with Therese Johaug of Norway and Finland's Aino-Kaisa Saarinen, stayed in a close pack for most of the skating phase with Johaug setting the pace in a bid to break the stronger finishers.
Just before the end Kalla and Bjørgen broke away with the Norwegian nordic superstar showing her sprinting prowess to ease to gold.
"I knew Charlotte would be strong in the sprint and she's good at the climbs but I thought that if I could follow her, I would have a chance," said Bjørgen.
"I knew it would be a sprint. I did my best for the last 100 metres and I was sprinting very hard at the end."
One of the big early favourites, Bjørgen's great rival Justyna Kowalczyk of Poland, tripped in the changeover area, along with several others who appeared to come into the zone too fast.
Even her huge stamina was not enough to catch her opponents and Kowalczyk finished an exhausted sixth.
In Vancouver, Bjoergen also won the skiathlon as well as the classic sprint and relay. But in a memorable duel, Kowalczyk pipped her in the 30 km mass start.
After the dominance of her performance in the skiathlon, Bjoergen may now want to reassess her target of just one gold medal.