Meanwhile fellow world championship hopeful Sophie Williamson (Central Otago-Wakatipu) took out the women's under 19 honours. Williamson, from Alexandra, won a world junior medal last year and also preparing for the Invercargill event.
It proved a strong day for the Pegasus club from Christchurch with Horgan claiming the elite men, Richard Lawson taking out the under 23 and Holly Edmondston winning the under 17 girls.
There was a fierce battle in the age groups as well. None more so than the men's 40-44 years, where Auckland's Aaron Strong edged out Gisborne's Peter Murphy by nine seconds with multi-national champion Gordon McCauley third. The illustrious trio were the fastest of all age groupers over the 25km journey.
There were none more impressive in the women's age groups than local Ramblers club rider Ingrid Perols, recovering from treatment for tumours in the brain, who won the 50-54 years age group by nearly a minute.
There was plenty of attention in the elite women's contest with the Olympic-bound pursuit group of Neilsen, Rushlee Buchanan, Lauren Ellis and individual pursuit world champion Alison Shanks competing.
Neilsen was pleased with her strong performance to clock 36:50 for the 25km distance with Buchanan third, Shanks fourth and Ellis seventh.
"It was a fun course. The sun showed up so it was fantastic," Neilsen said. "It was a great start for me. The course had a lot of texture in it although that hill on the way back was a bit nasty once you had some hurt in the legs.
"I enjoyed it. I was trying to concentrate on my computer and see what the legs would give me today.
"It's fantastic to have the whole team here and great to see so many people here taking part and watching."
The age group and masters road races begin tomorrow on a course near Taradale with elite women racing on Saturday and elite men on Sunday.