Rackham (19), who established a time of 1hr 15min 57sec in the Gore event last month, yesterday sliced 4min 11sec from his half marathon time, recording 1hr 11min 46sec, and finishing 2min 25sec clear of Otago middle distance champion Jonah Smith, who despite suffering the effects of hypothermia crossed in second place.
Steven Morrison was third in 1hr 20min 20sec.
The course was swept with sleet, hail and snow, and a wind chill of 4degC, and many competitors withdrew, suffering from hypothermia.
But Smith put the heat on early, setting a brisk pace that was challenged only by Rackham. The two were locked together for the first 15km, until Rackham decided to up the tempo with his mind on not wanting to be challenged up the hill to the finish.
''It was grind,'' Rackham said.
''I wanted to overcome the weather and get some distance on Jonah before the hill.''
Rackham made no secret of the fact he was pleased with his result.
''It all went to plan and I executed it quite well.''
Rackham, who resigned from a labouring job two weeks ago to focus on his running and finalise preparations for a scholarship to a United States university, will next target the men's under 20 title at the national cross country in Christchurch on August 1. From then on his future will be dependent on scholarship options. He hopes to get the nod for Boston University.
He has a personal best 1500m time of 3min 51.16sec, set in Wellington in March, after clocking the fastest time so far this year over 800m for a New Zealand under 20 athlete, with 1min 50.39sec in Auckland in February.
The objective of contesting yesterday's half marathon, his second in as many months, was built into his training schedule as part of his endurance work for the shorter 800m and 1500m distances.
At secondary school Rackham won back to back 1500m national senior secondary schools titles. He has a mile time of 4min 12.45sec and a 3000m time of 8min 49.29sec.
Auckland's Jacquline Eastman was first home in the open women's section of the half marathon, clocking 1hr 30min 47sec, Jordan Bone was second in 1hr 35min 2sec and Alice Barach third in 1hr 37min.
In the associated 10km event, it was a day for Dunedin based middle distance championships, as Bella Bloomfield won the open women's title in 41min 53sec, Melinda Cummings was second in 48min 58sec and Kiri Pullar third in 49min 20sec.
Dunedin triathlete and member of the national junior elite duathlon team for the world championships later this year, Jake Jackson Grammer won the open men's 10km event in 34min 57sec, an impressive time in view of the conditions. Ryan Shanks was second in 40min 25sec, and Luc Thomson third in 42min.
The associated 10km walk proved a competitive affair. Janeece Park won in 1hr 16min 11sec, holding out David Scobie, who finished in 1hr 16min 35sec. Kathy McKendry was third in 1hr 18min 31sec.
