The Hill City sprinter took the title at Wellington last season, when he pushed his training partner and the winner of the title for the previous three years, Cory Innes, off his perch.
The Otago runners filled the top two spots, Moore winning the title in 47.09sec from Innes in 47.74sec.
Moore, who came fourth in the 200m in 2008 decided to step up to the longer distance.
The training was not too different, because his coach, Brent Ward, emphasises speed and trains his 400m runners in a similar way to his 100m and 200m sprinters.
The most difficult part was to tackle the mental barrier.
"Physically, I know that I have the ability and it is just a matter of being able to run the distance," Moore said.
"It is just a matter of getting your head around it and not worrying about the pain."
Moore (25), a masters student in business and marketing at the University of Otago, gained confidence when he ran 46.95sec at Invercargill last February.
It was the fastest time in the country last season.
The Hill City flier has been troubled by hamstring problems and has not raced on the track this season.
He is being treated by the New Zealand athletics team's physiotherapist Helen Littleworth and plans to start racing next month.
"I want to run fast by the time of the New Zealand championships but will just have to see what happens. I want to hit my straps by the end of March."
The Commonwealth Games are not on his agenda, because he thinks the qualifying standard of 45.50sec too hard for him at the moment.
"The standards set by Athletics New Zealand are ridiculous. They are just too tough," Moore said, "I will just run as fast as I can and see what happens."
A more realistic goal for him is to focus on next year's world championships and the 2012 Olympic Games.
Moore wants New Zealand to qualify a 4x400m relay team at the London Olympics.
The team would need to average 46sec for the 400m.
"Someone would have to run 45 seconds to guarantee our spot," he said. "We need to develop more depth in the event."
The leading lights at the moment are Moore and Innes and they are backed by Aucklanders Matt Brown and Frazer Wickes.
A runner expected to step up is the promising Southlander Matthew Robinson, who won his third senior boys' title at the New Zealand secondary schools championships at Christchurch last month.
He has a best time of 47.78sec.
Moore spent six weeks racing in Europe last winter and had a best time of 47.10sec when he finished fifth at Mondo Keien in the Netherlands.
He also competed for New Zealand at the World University Games at Belgrade, Serbia, where he reached the semifinals.
Moore qualified in his heat when he ran 47.36sec but he was not able to follow it up in the semifinals the next day, when he ran 47.52sec and failed to qualify for the final.
"I wasn't used to the quick turn-around," he said. "I will have to get fitter to get back-to times."
The time in Europe was a big learning curve for Moore.
"The top runners are more efficient and run with good technique," he said. "But apart from that there is not a big difference between us."
Moore intends to return to Europe this winter to get more races than the six he had last year.
"I will go two weeks early to give myself time to settle in and get over the jet lag," he said.
Moore file
At a glance
Age: 25
Occupation: Masters student in business and marketing at the University of Otago
Sport: Athletics
Coach: Brent Ward
Record: NZ senior men's 400m champion 2009
Best times: 100m (10.60sec), 200m (21.27sec), 400m (46.95sec).
