Aussie Women's Eight all smiles after first Rio race

Australian rower Lucy Stephan says she had to wipe the smile from her face as the women's eight took to the water for their first race in Rio after their late Olympic call-up.

The crew finished last in their heat at Lagoa Stadium on Monday but were happy with their performance with only two weeks' preparation under their belts after replacing Russia in the field.

Stephan was set to be pounding the pavement in the Brisbane marathon over the weekend rather than rowing at the Olympics and was still pinching herself that she was in Rio.

"I took the first three strokes and I was like, `Wow, this is pretty cool' and I had a big smile on my face and I had to get my mind back in the boat," Stephan said.

"It's just an amazing experience and for our first two-kilometre race since qualification (in May) it was good to go out there and give it a red-hot crack.

"It wasn't the best preparation but we're taking the opportunity and going with it."

The Australians spent a fortnight training in Melbourne after receiving the news that as the fastest losers at the final Olympic qualification regatta in Switzerland in late May, they would take the disqualified Russians' place.

They only arrived in Rio during the opening ceremony and had to borrow a boat and oars to compete.

The crew will race the repechage round on Wednesday with only first-placed USA going directly from the heat to Saturday's medal decider.

The USA haven't lost an Olympic race or world championship since 2005, when they were beaten by Australia.

The Australians said it was actually a positive to have another race, in which they need to finish top four to advance.

In the heat they were three seconds slower than their last race in Lucerne.

"That's really not much at all and in the repechage we're going to improve again," Stephan said.