The 27-year-old was the first Australian into the Sambodromo, home of Rio's iconic carnival, in 18th place, clocking 2:30.53 in a race won by Kenyan Jemima Sumgong in 2:24.04.

Clark lives in Sydney but was born in Launceston, began running at East Launceston and St Leonards primary schools and was a member of St Leonards Little Athletics Club.

Her mother, Margaret, was a gymnast at the Commonwealth Games and world championships and her aunt, Liz Jack, went to the 1976 Olympics as a diver.

"I'm so proud to continue that on," Clark said.

"When you are running out there for a long time on your own you do think about your family and friends and your mum and aunt and everyone who has chipped in to make you who you are. It was good inspiration. I'm really happy and hope that they were watching and got a little bit excited and felt proud.

"I do feel a long way from Launceston but my brother David and his girlfriend Georgia are here from Launceston so I definitely felt the home love out there.

"I think deep-down I probably always will feel Tasmanian. They say you can take the girl out of Tassie but you can never take Tassie out of the girl."

Running just her second marathon in sweltering conditions, Clark couldn't quite repeat the 2:29.07 she recorded in Amsterdam to qualify for the Games.

"I wanted a PB but when I heard it was going to be hot I set my goal to come in the top 20, I've done that and I'm really thrilled with the way my race came together.

"I'm blessed because I'm pretty small so I handle the heat better than most people. I've practised a lot, I wore heaps of layers at home, I've run in the heat chamber so I was well prepared and I was able to take advantage of a few shady spots."

The former national steeplechase champion, who has lived in Germany, Indonesia and America since leaving Tasmania aged 11, said she was getting used to the 42-kilometre ordeal.

"Every time I line up I'm thinking 'why am I doing this?' but when I finish it's a good feeling to know that you've done the toughest mental and physical challenge out there,” she said.

“I'm sure there are more in me but when I don't know.

“Ask me again in six months."