McKeown was all business when she came out of the tunnel, marching to her block with eyes only on the prize at stake.

"The nerves were definitely there," she said.

"But I reminded myself that it's a pool in a different venue, and I train every single day of my life. 

Regan Smith was more flamboyant with her entry, taking the time to enjoy her moment, waving her arms and then slowly undressing at her chair. 

Keeping everyone waiting. Games, within games, letting those nerves build in her waiting adversaries.

With French women in the two outside lanes, the swimmers inside could have been lulled into the false security that they were anonymous to the majority of the crowd.

But the masses of Americans present made sure there was no doubt the interest was in the centre of the pool.

And McKeown knew. She knew where the threats were and knew exactly how she'd respond to them.

Bouncing on her toes before being allowed into the water, McKeown wasted no time in getting into her work once the buzzer went and the crowd roared.

She went out hard, holding the line along with the Americans to her right, Smith and Katharine Berkoff.

It was Canadian Kylie Masse in lane two who leaped out to turn first though, dead level with Smith, McKeown fourth behind Berkoff.

In the second 50m though, McKeown turned it on, drawn through by Masse, Berkoff and Smith, the four in a line through 75m with the race anyone's to win.

And that's where the racer comes in. 

That's where that little bit of a chip on the shoulder comes into play, that dogged unwillingness to be beaten when it really counts.

"I knew it was going to come down to the last five metres," McKeown said.

"We're both extremely good athletes, and both extremely good trainers, so it's just who feels better on the day, and she pushed me the whole way through. 

"You wait for the race and finish it, and I can't even remember it now."

Timing is everything in sport. Get it right and everything follows how it's meant to.  

McKeown was frustrated at trials for missing her world record by less than a tenth of a second.

Smith meanwhile, was confident that breaking McKeown's world record by a whopping 0.2 seconds in Indianapolis was "part of the plan".

Timing matters.

Here, McKeown swam the exact same time of her previous world record, 57.33, enough to claim the Olympic record and a fourth Olympic gold medal.

Smith was second just 0.33 seconds behind, Berkoff a further 0.32 behind her to round out the podium.

McKeown's reaction was typical of that racer, up on the lane rope, a punch of the air, before slapping the water with a burst of what looked a touch like relief.

Someone had come for her crown, and despite being put under enormous pressure, she saw them off.

With four gold medals, McKeown is now one of Australia's most decorated Olympians.