"I thought they were trying to squeeze that little bit extra out of me," Nielsen said. "It was a bit of a surprise. I was starting to get used to coming second which doesn't mean I try any less, it just always seems to turn out that way."
The Hamilton rider, bidding for a spot in the track team for July's Commonwealth Games in Glasgow, said the success was an indication that her preparations are on track.
"I have been doing a lot of strength work and that shows it must be working. There are definite things I still need to work on but it should work well for the track and I am looking forward to the rest of the season.
"Hopefully it progresses well and that earns me a spot on the team for the Commonwealth Games."
She won in 34.28 to be 28 seconds ahead of a disappointed Villumsen, who said she felt off her game throughout the ride, after an unusually early start to her season at the Bay Crits in Melbourne last week.
Tour de Vineyards winner Reta Trotman (Otago) was third in 35.02, just ahead of London Olympic track riders Lauren Ellis (Mid Canterbury) and Rushlee Buchanan (Waikato).
With defending champion Jo Cooper and three-time under-23 winner Michael Vink ruled out with injury and illness respectively, local rider Horgan assumed the favourite's tag.
He and Gunman were locked with identical times at the 20km turn around, but Gunman proved stronger coming back into the freshening breeze to clock 50 min 42 sec, with Horgan 12 seconds back.
Gunman's victory follows on from a strong performance finishing runner-up in the Tour of Southland.
"The year could not have started any better. Things started well at the Tour of Southland and I came away and refocused on my time trialling."
He drew motivation from last year's winner Cooper, who drove his support car today.
"I just wanted to show him what I could do. It was an inspiration to have him in the car and my folks too."
Former under-23 champion Jason Christie (Ashburton) finished third in 51:04 ahead of 2012 winner Paul Odlin (Christchurch).
Earlier, Gough, cousin of London Olympic track medallist Westley, also showed his strength into the breeze to win the under-23 battle. The Hawkes Bay rider clocked 51:38 to finish nine seconds clear of favourite Oram with his fellow Auckland rider Dion Smith third.
Gough competed with the New Zealand endurance track team and a Belgium combination on the roads of Europe this year.
He was delighted with his performance and hoped it would also transfer into a good showing in tomorrow's 185km road race.
Today is the elite women's road race over 120.5km which comprises eight laps with six climbs of the infamous Dyers Pass in the Cashmere Hills.
The elite and under-23 men's race tomorrow is 12 laps in total for 183.7km, starting with the usual full lap on the flat before 10 circuits up the Dyers Pass climb and a final flat lap to the finish.
