Thorburn's torrid pace over the first 2km circuit of the 12km course eased the threats posed by most of his main rivals in a field that contained many of Otago's top middle and long distance runners.
Maintaining control through his strong front-running tactic, the size of his lead until the midway stage of the race fluctuated, as those being dragged along in his wake struggled for momentum.
Only Callan Moody, a past junior champion on the course and a runner-up three years ago to Ariki clubmate Matt Lambert, managed the early pace by Thorburn with any success, arriving on Thorburn's shoulder at the halfway stage.
Little separated the pair as they each put in surges in an attempt to break the other.
These tactics served to increase the lead over last year's runner-up, Bevan Stevens (Caversham), and Peter Meffan (Caversham), who was running the race of his life in an attempt to claim the bronze medal.
Thorburn and Moody continued to dominate up front, until Thorburn caught his second wind and snatched a tentative 2sec lead entering the final 2km. He took to the hill section for the sixth and final time as if it were his first, stretching his lead out to 8sec over Moody, with Stevens and Meffan still battling for bronze 30sec further back.
Moody's confidence grew when he noticed Thorburn glancing back over the final 1500m and the race virtually turned into a sprint from both runners. Thorburn crossed the finish line in 39min 55sec with Moody 5sec back in second.
"That was a race," an ecstatic Thorburn said.
"Nice to do a sub-40 as well."
Thorburn knew his approach to the race was a gamble that could have been his undoing.
"I knew I had to do it to break the race up and get the jump on the speed boys. I thought I was toast when Callan came up on me. But in the end it helped and meant I could grab the race when I wanted it."
Stevens claimed third in a dramatic dive for the line in 40min 38sec. There was consolation for Stevens as he headed a Caversham quartet that consisted Meffan, Daniel Balchin and Tony Payne, to win the interclub teams trophy.
A late decision to defend her title paid off for Rachel Kingsford (Hill City) as the young cross-country international dominated the open women's field to win in 30min 31sec on the 8000m course, with Kirsty Morris (Leith) second in 31min 48sec and Emily Soisberg (Wellington Scottish) third in 32min 44sec.
Little has been seen of Kingsford this season due to heavy university commitments and despite appearances for Hill City in the Lovelock and Ponydale relay events, any further competition this year will depend on her studies.
The junior titles were keenly contested with Anthony Trainor (Ariki) winning the junior men's title and Shauna Pali (Hill City) the junior women's.
Sian English (Ariki) and Sam Bremner (Hill City) proved they are senior champions in waiting when they each recorded impressive victories in the under-16 grade.
