In lane three, the world record holder. In lane four, the world champion. In lane five, the Olympic champion.

The women’s 400m freestyle final at the swimming world championships, which began in Fukuoka, Japan on Sunday, had been described as the Race of the Century. That was a label last given to a famous 200m freestyle duel 19 years ago, at the Athens Olympics, featuring swimming legends Ian Thorpe, Michael Phelps, Pieter van den Hoogenband and Grant Hackett.

This edition offered an equally exhilarating battle. Canada’s Summer McIntosh turns 17 next month – and the teenage prodigy already held the world record. McIntosh had taken that record off Australia’s Ariarne Titmus, 22, who won Olympic gold in Tokyo two years ago.

And in lane four, sandwiched between her rivals, was USA’s Katie Ledecky. A seven-time Olympic gold medallist and 19-time world champion, Ledecky is widely-regarded as the greatest female swimmer ever. She entered the race as defending champion, having regained the crown in Hungary last year.

Ledecky had qualified fastest; McIntosh broke Titmus’s world record just months ago. If anything, it was Titmus – who had been sluggish by her own standards at the Australian trials – who seemed vulnerable. It had the air of an era-defining race, the present and future of women’s middle-distance swimming going head-to-head for the first-time since Tokyo, possibly for the last time until Paris.

The 400m stands out for its blend of speed and endurance. It requires a stamina that sets it apart from the 50, 100 or 200m events, but a pace – particularly the ability to turn on the afterburners entering the final lap – that is not seen in the 800 or 1500m. It is a race of truth; a unique test of tolerance for pain.

In their last clash, two years and a thousand kilometres away at the Tokyo Aquatics Centre, Titmus was tactical. McIntosh led out, touching first at the first turn, before Ledecky surged forward. The American had a body-length advantage on the Australian for most of the race, before Titmus exploded with two laps to go. They touched together at the final turn, and Titmus swum away to gold.

On Sunday, it was Plan B. “Summer and Katy are both class acts, there are hardly any faults in their racing,” Titmus said afterward the race. “So I knew the only way to try and take the win was to take it out.”

Titmus turned in second after the first 50m. Then she did not look back. The Australian led for the remainder of the race to break the world record and become the first woman ever to go below the three minutes and 56 second mark. McIntosh’s prior record was eight one-hundredths of a second above that mark – Titmus demolished it, finishing in 3:55.38.

“I came in tonight and just tried to be fearless, race like I was that little girl again,” Titmus said after the race. “And it paid off.”

Titmus’s short career to date has already been glittering: she is a former world champion and reigning Olympic and Commonwealth champion. But her performance in the race of the century was something else – not just winning it, but leading for almost the entire contest and leaving Ledecky and McIntosh in her wake. This was not just a win; it was a coronation. Ledecky finished second, more than three seconds behind Titmus, while New Zealand’s Erika Fairweather pipped McIntosh for bronze.

Even the usually understated Titmus admitted her triumph was something special. “This victory is my most satisfying,” she said. Her coach Dean Boxall, famous for going viral with his celebrations in Tokyo, did not need any encouragement to celebrate wildly.

It was a golden night all-around for Australia, with Sam Short winning the men’s 400m freestyle and setting the fourth-fastest time in history. The Australian women then smashed their own world record to win gold in the 4x100m freestyle – taking a remarkable near-two seconds off the time they set at the Olympics. The Australian men rounded out the evening, emerging surprise victors in the tightly-contested 4x100m freestyle, thanks to an impressive anchor swim by Kyle Chalmers.

The four gold medals surpassed Australia’s previous best-ever day at a world championships. The only sour note was Kaylee McKeown, a gold medal contender, being disqualified in the individual medley semi-finals.

With 12 months to go until the Paris Olympics, these world championships foreshadow some of the mouth-watering clashes to come – and hint at Australia’s current dominance in the pool.

McIntosh is only getting faster as she reaches her physical prime, while few would write-off Ledecky from a resurgence. But for now, it’s advantage Titmus, who did not just win the race of the century on Sunday but made it her own.