The reigning Olympic champion trailed by 0.08 seconds at the turn before powering home to win comfortably.

“I have never been this shaky in my life,” McKeown told this masthead. “I felt like I needed to vomit before my race. My old coach used to say, ‘if you’re nervous to that extent, you care about what you do’. I really channelled that and did what I could.”

McKeown is one of the most consistent swimmers on the Australian team. Her propensity to consistently clock fast times is admired by those who work with her closely.

“It was just a real testament to myself dealing with what I have over the past few hours,” McKeown told reporters. “I am really happy to have the Americans chasing me because I don’t think without them, I would have swum as fast as I did. It was great having them by my side.

“I just wanted to prove to myself that I am still swimming fast. I dug deep and gave it everything I could. ”

Earlier, there was a major upset from the first race of the night, when Romanian star David Popovici failed to win a medal in the men’s 200m freestyle after going in as the overwhelming favourite.

Popovici, who won this event at last year’s world championships in Budapest, led at the 150-metre mark before fading in the last few metres.

Great Britain made it a quinella, with Matt Richards (1:44.30) just hitting the wall ahead of teammate Tom Dean (1:44.32). Popovici’s time of (1:44.90) was almost two seconds outside his personal best.

Meanwhile, Australia’s Lani Pallister went into the women’s 1500m freestyle final as the third-fastest qualifier but finished fifth in a time of 15 minutes, 49.17 seconds, behind American legend Katie Ledecky (15:26.27) in first place.

“I’d be lying if I said I wasn’t a little disappointed,” Pallister said. “It’s just over my best time from last year (15:48.96) but as you get older you mature and you go through different things. I really put it on the line. I know I’m more capable than that.”

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Ledecky will come up against Ariarne Titmus later in the week in the 800m freestyle, having just been beaten by the Australian in the 400m freestyle final on Sunday night.

“She’s such a great racer,” Ledecky told this masthead. “She always steps up in these big races and big moments. It’s always a thrill to race her.”

Meanwhile, Titmus (1:54.64) and Mollie O’Callaghan (1:54.91) comfortably qualified for the women’s 200m final, which will feature Canadian young gun Summer McIntosh, who will be looking to make amends after her fourth place in the 400m freestyle.

Could Australia go 1-2?

“That’s the perfect scenario,” Titmus said. “I would love for that to happen. It’s a tough field and I think it will be fast.”

Watch the World Aquatics Championships in Fukuoka live on Channel Nine & 9Now.

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