Campbells doing it for themselves at Rio

Don't call Cate and Bronte Campbell Australian swimming's sister act at the Rio Olympics.

Comparisons with tennis' Williams siblings don't go down well, either.

Sure, the Aussie girls love each other.

And they fantasise about celebrating 4x100m freestyle relay gold at Rio side by side on Saturday's opening night of pool action.

But the Campbell sisters admit they will be doing it for themselves when they eyeball each other on the blocks at the 2016 Games.

"It is a selfish sport - when I am racing it is all about me," former world champ Cate Campbell said.

Sisters have never claimed gold and silver medals in the same event at an Olympic Games.

That may all change when world champion Bronte takes on sibling Cate in the 100m freestyle at the Rio Games.

Especially after Cate Campbell recently shattered German Britta Steffen's 2009 supersuit 100m world record at their final Rio warm-up while an ill Bronte rested at their shared Queensland home.

"I was proud and a little bit astounded," Bronte Campbell said of her sister's milestone.

"It was something we didn't think would happen - I certainly didn't expect it.

"I got a phone call about it from my dad and I thought my dad was joking.

"We are all here to compete and that doesn't change things for me.

"It's about what happens on the night.

"I see her training every day and I know what she is a capable of but it doesn't change anything for me."

Rio will mark the Campbell's second Games together.

"In 2012 when we qualified together in the 50m freestyle we knew we had achieved something great," Cate Campbell said.

"This time round it was as special.

"To be honest I am almost more excited racing alongside Bronte in the 4x100m relay."

Their bond is clear.

But they quickly shut down reporters trying to draw a line between them and tennis' Williams sisters.

"I think it is very different to Serena and Venus Williams," Bronte Campbell said.

"We are not playing against each other, we are in a pool with six others in a race.

"I am not racing against Cate. I am racing against myself.

"I am trying to do my best race."