'I saw something tick': Mollie O'Callaghan backed to topple Ariarne Titmus in blockbuster 200m final

Mollie O'Callaghan has been backed to topple Ariarne Titmus in the women's 200m freestyle final as the friendly rivalry between the two Aussie superstars heats up in Paris.

Titmus recently snatched the world record away at the Olympic trials, lighting a fire under O'Callaghan that has her primed for a massive push for gold at the Games.

In their semi-final meeting, Titmus finished slightly faster than her sparring partner, but there's reason to believe O'Callaghan can take it out when it matters most.

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Speaking on Stan Sport's Paris Preview, three-time Olympic gold medallist Grant Hackett predicted that the 20-year-old will prevail in the early hours of Tuesday morning (AEST).

"I am going to say Mollie [will win]," he said.

"Her focus is on the 200m and getting the world record back. It's going to be very, very close. I think Mollie is going to get her hand on the wall first this time.

"I know Mollie very well - she is very relaxed, she is a funny girl, but she is an intense competitor. Her focus on the 200 and getting that world record back has been huge.

"I'm sure they are both going for it all the time, but there'd be a healthy respect there."

O'Callaghan has already claimed one gold in Paris as part of the successful relay team, while Titmus overcame fierce rival Katie Ledecky in the 400m final.

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With the Aussie duo in close quarters at St Peters under the guidance of coach Dean Boxall, the intensity has risen to an entirely new level in recent months and according to head of sport Shaun Nodwell, one of the swimmers will reap the benefits.

"To be the best, you've got to beat the best," he said.

"It's been quite strategic how they do train - they know how fast each other is training, but they are not training directly against each other. They're always keeping an eye on what they're doing … it's pushing them more and more.

"Even recently, seeing Ariarne break Mollie's world record in trials, I saw something tick in Mollie and that stirred her on and it's going to lead to some fast swims.

"Dean's got a really good handle on the squad and the fact that he's got 10 or 11 swimmers over here, they all know how to push each other's buttons and when to have a break from each other.

"It's a really friendly relationship that they've got, but they also respect each other's privacy at the same time." 

Titmus and O'Callaghan are slated to compete in the final at 5.40am AEST.