Australian triathlete Penny Slater has described her 13th placing in the famed Hawaiian Ironman as an "amazing feeling".

Slater was the fastest finisher among a six-strong Australian contingent in Sunday's Ironman World Championship in Kailua-Kona, Hawaii.

In her second outing in the gruelling event, the 27-year-old from Canberra clocked eight hours 57 minutes 17 seconds - more than 30 minutes quicker than her 24th place on debut last year.

"It's a pretty amazing feeling," Slater said.

"I had the best day I could have, apart from the drafting penalty on the bike.

"It's one of those performances where you're like, 'I think I have it in me' but you don't know until you actually do it.

"It was really special to be riding and running alongside so many girls who I have looked up to for such a long time."

Slater improved her position throughout - she was 27th out of the water after the opening 3.8km swim but incurred a five minute penalty for drafting midway through the 180km bike leg.

Entering the 42.2km run course in 19th spot, Slater then gained further ground.

"I just got to work on the run ... I was trying to play the long game," she said.

"I ran up to a group of girls, there was five of us running together for five k's. I have never really been in a run battle like that and I came out on top, which was nice."

Great Britain's Lucy Charles-Barclay (8:24:31) won the world-renowned race from German Anna Haug (8:27:33).

Australia's Chloe Lane (9:28:31) finished 34th ahead of compatriots Sarah Crowley (35th, 9:35:11), Kate Gillespie-Jones (38th, 9:43:05), Laura Brown (39th, 9:48:01) and Sarah Thomas (42nd, 10:04:10).