"This is such a great event, I reckon this is New Zealand's equivalent of the famous escape from Alcatraz race. It has such history and is so tough," Ellice said.
"The swim was brutal, there were some real lulls out there in the water and then some big swells, you had to work the swells hard and time your moves but I enjoy the surf much better, I reckon, than the flat water stuff in most races.
"I spent the first part of the bike trying to sort out a few issues with my bottle system but eventually I wound into my work.
"I left a bit of work to do on the run and to be honest at the first lap on the run when Mark still had a minute on me I wondered if I would catch him.
"But I showed the benefits of some solid training and have overcome a calf strain that I had in November and was able to run fast today.
"There is nothing like feeling fit and running fast in the sport of triathlon."
Nielsen took out the women's race from Maddy Brunton, with first round winner Rachel Hamill third.
The win for 18-year-old Nielsen was a timely boost as the athlete prepares for the Australian Youth Olympic Festival later this month. The former ITU World Elite Junior champion looked composed throughout.
The day saw close to 600 participants across all race distances, from the hugely popular and sometimes manic kids Contact 1:2:1 to the beginners 3:9:3, and the more established sprint and standard (Trophy) distance events, including a strong turnout of teams.
Contact Trophy (standard distance)
1500m swim, 40km bike, 10km run
Men
Clark Ellice (New Plymouth) 1:55:47 1
Mark Bowstead (Auckland) 1:56:02 2
Hamish Hammond (Greytown) 2:00:19 3
Michael Poole (USA/Auckland) 2:00:49 4
Sam Franklin (Auckland) 2:02:39 5
Women
Mikayla Nielsen (Waikato) 2:13:50 1
Maddy Brunton (Waikato) 2:16:52 2
Rachel Hamill (Waikato) 2:19:49 3
Hannah Lawrence (Auckland) 2:21:59 4
Anna Lorimer (Auckland) 2:22:44 5
Contact Sprint
750m swim, 20km bike, 5km run
Men
Tayler Reid 1:00:28 1
Cameron Todd 1:01:39 2
Alexi Petri 1:02:39 3
Women
Sam Warriner 1:04:41 1
Elise Salt 1:07:35 2
Jaimee Leader 1:08:26 3
Contact 3:9:3
300m swim, 9km bike, 3km run
Men
Adam McArthy 34:13 1
Louis Poot 36:40 2
Jeremy Shaw 36:43 3
Women
Anna Wilkinson 39:49 1
Prue Bolt 41:10 2
Hannah Knighton 42:49 3
Contact 1:2:1 (Children)
100m swim, 2km bike, 1km run
Boys
Oliver Gordon 8:54 1
Josh Marryatt 8:56 2
Jack Laker 9:06 3
Girls
Jemma Cherguit 9:25 1
Ava McKenzie 9:47 2
Emma Leader 9:51 3
- APNZ