He recorded 30min 13.84sec to head off Michael Voss,who finished in 30min 24.44sec. Oska Baynes was third.
Cromwell runner Daniel Balchin was fourth in 30min 51.89sec, a personal best.
Shields who has shifted back to New Zealand after a stint in Melbourne will now be based in Christchurch where he enjoys the hills in training.
He was ecstatic on crossing the finish and said he race had gone to plan.
"These opportunities don't come that often so I was going to enjoy it. I worked hard for it. The last 5km was exactly how I wanted it to go,'' he said.
"I had a vision that I was going to take them to task over the last 5km and see if they could go with me, and if they could and I got beaten I was OK with that. But I wanted to throw it down and see if I could challenge myself and not only the rest of the field.''
