Villumsen won from 22-year-old Sharlotte Lucas, with veteran Nelson cyclist Karen Fulton out-sprinting national representative Emily Collins for third.
Olympic and Commonwealth Games track specialist Lauren Ellis made the first move when she opened a 40-second lead on the second lap, setting up the target for her fellow New Zealand representatives Villumsen and Jaime Nielsen to chase.
The pair bridged the gap and overtook Ellis on the climb up Dyers Pass on lap three but Nielsen, who beat Villumsen in Friday's time trial, succumbed to the efforts and hot conditions at the top of the climb on the next lap and withdrew.
"I thought it was a bit early," Villumsen said. "I wanted her to get over the climb and work together for at least another lap or two. But I must have had pretty good legs today. It's great to have the national jersey to wear for my new team this year."
From that point, Villumsen took complete control, extending her lead from three minutes on lap three, increasing the margin on every lap.
It was a complete master class from the cyclist who has won five world championship medals, was fifth in the Beijing Olympic road race and fifth at the Commonwealth Games in Glasgow. She enjoyed a good 2014 road season, including eighth in the road race at the world championships, victory in the Tour of Ardeche and 13th in the women's Tour de France.
Lucas, the Canterbury champion, broke away from the chase bunch on the final lap for her second placing, while Fulton outsprinted Collins in what she said was her final time at the elite national championships.
The elite and under-23 men's race over 183.7km will be contested today. Track convert Paddy Bevin is among the pre-race favourites in the elite race, which also features World Tour riders Sam Bewley, George Bennett and Jesse Sergent.