Filmer (17) had beaten his opponents by the time he reached halfway but he still had to conquer the steep slopes on the Signal Hill course.
"The steep hills were hard and I was tempted to stop and rest," he said. "My legs were aching but I kept going."
He refused to give in to the mountain and demonstrated his tenacity on the steep and awkward rocky section near the finish that was difficult to ride over.
He picked up his bike and ran over the rocks on the tricky section and then hopped on again and rode the final 50m to the finish.
Filmer won by 43sec in the fast time of 12min 12sec from Oceania champion Gavin McCarthy (Upper Hutt) in 13min 05sec and Luke Osborne (Hastings) in 13min 17sec.
The women's title was won by Kate Fluker (Queenstown) in 16min 16sec from Raewyn Morrison (Wellington) in 17min 20sec.
Woodvilles Gareth Cannon (14) won the under-17 title in 14min 04sec and was fourth to finish.
Cameron Howell (Palmerston North) won the under-15 title in 15min 21sec.
It was the first individual New Zealand title for Filmer, a pupil at Waimea College, who has only been mountain biking for two years.
He became enthusiastic about the sport when he was a member of his school team that won the national secondary schools relay title last year.
Filmer started slowly and did not take the lead until 500m up the hill. He was not able to shake off McCarthy until halfway.
"He spun his wheels too quickly at this stage," McCarthy (32), a bike mechanic, said.
McCarthy won his second Oceania uphill title in Dunedin last year but had to be satisfied with his third runner-up spot at the New Zealand championships.
He was awarded the senior men's title because Filmer qualified to win the junior under-19 title.
But this was a hollow title because all the glory goes to the first man to the top.
Osborne (26), a Hastings builder, finished third in his first year of racing mountain bikes and was second in the senior men's grade.
Tim Rush (20), an Oamaru mechanic, finished fifth overall and was third in the senior men's race in 14min 23sec.
Fluker (23), a Queenstown real estate agent, also started in conservative fashion and was lying third in the women's race until the third corner.
Fluker, in only her first year of mountain bike racing, grew increasingly confident as she ascended the hill.
It was in the last third of the race that she moved away from Morrison and won the women's race by 1min 04sec.
Morrison (21), a physiotherapy student, could not match the stamina of Fluker as she applied extra pressure on the upper slopes.
The open men's dual slalom title was won by Reon Boe (Queenstown) from Dave du Plessis (Perth) and Adrian Loo (Invercargill).
The junior slalom was won by Dan Franks (Christchurch) from Brian Baufils (Tahiti) and Dan McCombie (Dunedin).
