Vos held off Britain's Elizabeth Armitstead in a sprint finish on The Mall with Villumsen finishing officially in 18th place.
A split-second decision meant Vos finally struck road race gold after years of taking silver at the world championships.
Second at the worlds every year since 2007, the Dutchwoman rode an aggressive race and made the right moves when it mattered.
Vos launched her sprint some 150 metres from the finish line, jumping past bronze medallist Olga Zabelinskaya of Russia.
Lizzie Armitstead was in her wheel but Vos's move was too sudden for the British rider to follow.
"I was not confident because she (Armitstead) is very fast. I knew I had a big chance but I was also aware that if I made a little mistake Lizzie would be there," Vos told a news conference
"I had to choose the right moment and I think I did.
"You have to make your choices during the race. I knew there were going to be opportunities."
Vos, a successful track cyclist who won the 2008 points race Olympic title, made the most of hers.
She wanted a hard race and the Dutch team repeatedly wore the peloton down with attacks during the 140.3-km race.
"I knew it was 140 kilometres and I would need energy for the finish but I also knew that a hard race was good for me," Vos said.
"Others had to follow and spend energy, too. We had planned to attack early and many times to tire the others."
Countless times Vos and others tried to break from the pack only to be reined in but some 50 kilometres from the end, she and three others powered away.
"I felt good, we made it a hard race with the Dutch squad with early attacks," she explained.
"That was the plan. Then, during the race, I felt well this might be the day when everything comes together."
Vos's win crowned a season hampered by a collarbone fracture.
"You can't predict everything in cycling," said the 2006 road race world champion and a five-time cyclo-cross world champion.
"My preparations were troubled because of that broken collarbone but after four weeks I could race competitively again."
Back on the bike at the end of June, Vos won the Giro Donne, the women's version of the Giro d'Italia, claiming five of the nine stages.
Maybe Sunday's victory was predictable, after all.
