10/08/2016 10:45 AM AEST | Updated 11/08/2016 8:17 AM AEST

Australia's Ultimate Odd Rio Olympics Swimming Couple Lines Up For Gold.

One's big, one's small. One loves footy, one loves physics.

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They're great mates.

It's on. The big individual event of the pool for the blokes. 12.03 pm Thursday, Eastern Australian time. The men's 100m freestyle final at the Rio Olympics. Big men. Big egos. And in the case of the Aussies, one giant contrast.

Australia is represented in this race by the ultimate swimming odd couple: Kyle Chalmers and Cameron McEvoy. They could scarcely be more different if they were a cat and a dog.

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His feet barely fit on the blocks.

Chalmers, 18, is still in school (and his classmates delighted in watching him win bronze as part of the 4 x 100m freestyle relay earlier this week). He still has half an eye on a career as an AFL player when he's done with this swimming business.

McEvoy, 22, is a budding physicist. He used part of a press conference here in Rio last week to talk about the dipole moments of biomolecules. He tweets kooky stuff like this.

In person, Chalmers is all arms and legs. He had size 15 feet when he was just 13-years-old and his frame seems as wide as a doorway. McEvoy is no shorty at 185cm, but he's much more compact. He looks like a shrimp next to Chalmers.

Their racing styles are complete opposites too. Like all teenagers, Chalmers is slow to wake up. He was last at the 50m mark in his heat here in Rio, yet won it. He was seventh at the halfway mark of his semi, at which point even seasoned swimming watchers found themselves thinking 'uh-oh". But he won that race too.

McEvoy is more even-paced. He races near the lead and generally stays there.

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He's not exactly small, but compared to Kyle he's a bit of a midget.

Is Chalmers worried about his slow first laps? the Huffington Post Australia put that question to him overnight in Rio, and he answered in that typically unflappable happy-go-lucky way of his.

"That just how I swim," he said. "I swim to my strengths and my strengths is my back end. When I turn at the wall, I know I've got that back end.

"Those guys might have held a second in front of me at the turn [in the semi], but I worked my butt of to get on that wall in the end. So I'm happy where I'm at. But in the final, I'll work the first 50 a little more."

Reuters Photographer / Reuters
He is an absolute BEAST in the water.

God help the rest of the world if Kyle Chalmers swims a fast first 50 and backs it up with his usual blistering second 50. As for McEvoy, expect him to lead and -- hopefully -- stay there.

But of course, it likely won't be that easy. After a great first night at the Rio Olympic swimming competition -- when Mack Horton held off drug-tainted Chinese swimmer Sun Yang to win the 400m freestyle and the Campbell sisters anchored our golden women's 4 x 100m freestyle relay -- Australia has had some disappointments in the Rio pool.

World champions Mitch Larkin and Emily Seebohm both missed the podium in the 100m backstroke. There's no guarantees of anything in any race, especially one as keenly contested as this.

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Here's hoping his biomolecules are firing today!

America's Nathan Adrian won this race at the London 2012 Games. He's the guy who beat James Magnussen by half a fingernail, or 0.01 of a second in technical terms. Yet Adrian almost bombed out in Rio. He was the slowest of all the semi final qualifiers. Then he blitzed his semi from lane one, narrowly beating McEvoy and qualifying fastest for today's final.

Will Adrian win again? Or will someone else do the business? This has not been a favourite's race in recent Olympics. But in the race of Australia's dreams, McEvoy leads with 25 metres to go and Chalmers churns through the water with those giant propellors he calls his limbs.

They hit the wall... and? We'll leave that up to your imagination.

One thing we can say for sure is these two are great mates. They're actually rooming together at the Rio Athletes' Village.

"I love Cam, he's probably one of my closer mates," Chalmers said. "We've got along really well living in the same apartment this week and sharing experiences, He's been a guy i can look up to and ask questions whenever I need to , so I'm very, very excited to be in the final with him."

We're excited too.

Meanwhile the women had their 100m freestyle heats today, and there were no surprises when Cate Campbell swam a new Olympic record of 52.78s to qualify fastest for the semis. Little sister Bronte came home strongly to post a time of 53.71s, qualify her in eighth spot for the semi-finals.

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