Taupo's Bevan Docherty has won the NZ Ironman, setting a course record at his first attempt of 8 hours, 15 minutes, 35 seconds.
Second was Estonian Marko Albert, and third was Cameron Brown.
Docherty took almost three minutes off 10-time winner Cameron Brown's previous course record to blitz the field and score a stunning win.
Docherty, a two-time Olympic medallist quit the ITU Olympic distance triathlon scene last year to take on a new challenge.
Docherty had a 2min 20sec lead over Albert after the 3.8km swim and 180km cycle legs in very hot and still conditions.
Docherty said before the Kellogg's Nutri-Grain sponsored event he was heading into the unknown and was uncertain about his nutrition and pacing plans - two important factors in the long-distance event. His swim was excellent; he exited the water in second place in 45min 44sec, 10 seconds down on Albert, and he looked very relaxed in both the first and second transitions.
Kiwi Terenzo Bozzone was handily placed in the early stages of the bike leg but has slipped off the pace a little to lie fifth behind fourth-placed Courtney Ogden, of Australia.
As expected, it's a two-athlete race in the women's event. American Meredith Kessler pulled off a stunning swim to exit the water in fourth place overall - more than four minutes ahead of Kiwi Gina Crawford.
Crawford slowly took time out of Kessler on the first half of the bike leg but the American pulled away on the second half. The time gap was 1min 15sec at the 70km mark but the gap went out to 5min 36sec at 135km.
There are 30 professionals in the event and a big age group contingent of about 1300. In perfect conditions on the lake, no athlete failed to make the 2hr 20min swim cut-off time.
Earlier story: Taupo's Bevan Docherty has stamped his mark in his first attempt at this year's Ironman New Zealand.
Racing on home soil and in what organisers are calling near perfect conditions Docherty has taken more than a minute's lead at the 150km mark in the cycle leg of the event.
More than 1400 competitors took to the water this morning for the 3.8km race. Docherty was the second competitor out of the water 10 seconds behind Estonia's Marko Albert whose time was 45m 34s. Terenzo Bozzone was third in a time of 47m 22s with Cameron Brown in fifth in a time of 50m 15s.
In a startling outcome American Meredith Kessler was the first woman out of the water in a time of 47m 37s and fourth overall. She was followed by New Zealand's Gina Crawford in a time of 51m 44s and Australian Carrie Lester 54m 40.
With all elite competitors out of transition in quick time, riders settled into a relatively quick pace. Docherty took the lead from Albert at the 76km mark and maintained the lead right through till the run. Docherty put on the after burners at the 150km mark to take more than a minutes lead on Albert with Brown taking third spot 9m 53s behind.
In the women's race Kessler has looked strong for the entire cycling leg opening up more than 5 minutes on Crawford and 15 minutes on Lester.
With temperatures in the high 20s expected to take its toll on the athletes in the 42km run but with little wind to slow runners down. Organisers are expecting the first runner home about 3.15pm.
Update:
Terenzo Bozzone has withdrawn while Bevan Docherty remains in control of this year's New Zealand Ironman.
Bozzone has had to withdraw from this year's Ironman after only 10km into the 42km run. Reports indicate the athlete was struggling right from the start of this morning race and despite being in the top 10 it appeared the 23C heat has taken its toll on the athlete.
Taupo's Bevan Docherty remains in the lead at the 10km mark of the run and was 4 minutes and 25 seconds ahead of Marko Albert from Estonia with Cameron Brown chasing 12 minutes and 18 seconds behind in third.
American Meredith Kessler still leads the women's race with Gina Crawford more than 8 minutes behind 5km into the run.
Indications are if Docherty continues at this pace he is expected to cross the finish line around 3pm