Olympics-Swimming-'Nervous wreck' O'Callaghan takes down teammate Titmus

PARIS - Mollie O'Callaghan was crippled by nerves, unable to sleep and overthinking her 200 metres freestyle battle with Australian teammate Ariarne Titmus, but the redheaded Queenslander turned cold-blooded predator when it counted in the Paris pool.

O'Callaghan won her first individual Olympic gold medal on Monday in a showdown with the defending champion and one of the nation's great swimmers, who only weeks before had broken her world record at Australia's trials in a psychological blow.

"Today, I was a nervous wreck. I couldn't nap, couldn't do anything," O'Callaghan told reporters.

"My brain just overthinks.

"I've got so many words in my head to overcome the nerves and they're still there because I've got so much more to go."

Beating Titmus in a race inevitably means winning a title.

A year ago, O'Callaghan stunned Titmus to win the 200m freestyle world title in a world record time at the Fukuoka World Championships.

But the Tasmanian nicknamed "Terminator" was in ominous form after defending her 400 metres gold on day one, turning what was hyped as the "race of the century" with Katie Ledecky and Summer McIntosh into a convincing win.

Swimming fans would love to know what pep-talks Boxall gave each of his swimmers before they faced off on Monday.

Their strategy appeared similar, relying on back-end speed to haul in Hong Kong's eventual bronze-winner Siobhan Haughey.

But it was O'Callaghan finding the extra gear to secure her fourth Olympic gold medal and fifth overall.

There may be a fifth gold coming up for the Brisbane native when she swims in the 100 metres freestyle -- all at the age of 20.

Humbled, Titmus shed tears but was gracious in defeat.

"These are happy tears, honestly," said Titmus after winning her sixth Olympic medal.

"It's really hard to hold your emotions in in these situations. I know what it's like to be Olympic champion and I'm honestly happy for her.

"I'm really happy to be on the podium. I had nothing to lose tonight. I'm Olympic champion forever in the 200 and the 400."