Katie Ledecky of the U.S during training [Source: Reuters]

Every Olympics has its defining sporting moment such as Usain Bolt in the 100 metres at the 2008 Beijing Summer Games or Sydney Crosby’s golden goal for Canada on home ice in Vancouver in 2010.

Some appear as if out of thin air. Others can be scheduled, as in Paris where on the opening night of competition on Saturday at the La Defense pool three world record holders could get the Summer Games off to an explosive start in a women’s 400 metres freestyle showdown already being hyped as a “Race of the Century” candidate.

The United States’ Katie Ledecky, already rated one of the greatest swimmers of all-time, Australian torpedo and current world record holder Ariarne Titmus, and Canadian teen sensation Summer McIntosh are set to light up the Paris night in a race for gold that may produce a swim for the ages.

Personalities make compelling rivalries and the three women, all in different stages of their careers, come to Paris giving off different vibes.

Ledecky is the elder stateswoman, a seven-time Olympic gold medallist who chooses her words carefully not wanting to provide added motivation in a race that could be decided in the blink of an eye.

McIntosh, who made her Olympic debut in Tokyo at just 14-years-old, has matured into a poised competitor but her confidence in the pool is contrasted by an uneasiness in the spotlight.

Titmus brings confidence that sometimes borders on cockiness to the deck, respectfully assuring that Ledecky would not have it all her way in Paris.

What the trio have in common is they all swim fast. Very fast.

At different times Ledecky, Titmus and McIntosh have owned the 400m free world record, and combined they have posted the top 28 times ever in the event.

Ledecky claimed the 400m free gold at the 2016 Rio Olympics with Titmus knocking the American from top spot on the podium into second place in Tokyo.

McIntosh has yet to set foot on an Olympic podium but that is expected to change in Paris where the now 17-year-old is set to compete in four individual events: 200 individual medley (IM), 200 butterfly, 400 free and 400 IM, where she is the world record holder and a double world champion.