The swimming world on Monday was left awestruck on a dramatic opening night of the World Championships as France's rising star, Leon Marchand, delivered a jaw-dropping performance, shattering Michael Phelps's last remaining world record in the 400-meter individual medley.

Meanwhile, Australian sensation Ariarne Titmus left her rivals gasping for breath in the women's 400-meter freestyle to reclaim her world record.

Marchand's pursuit of glory paid off in a breathtaking fashion as he clocked 4 minutes 2.50 seconds in the 400-meter individual medley, carving more than a second off Phelps's long-standing record of 4:03.84, which had remained unchallenged since the 2008 Beijing Olympics.

The young French talent has been hailed as one of the faces of the upcoming Paris Olympics.

"It was insane," an exuberant Marchand exclaimed after the race. "That was one of the most painful things I did. That was amazing to do it here. The time is crazy."

Phelps, the legendary 28-time Olympic medalist, who was present at the event, was not only impressed by Marchand's record-breaking feat but also provided the French starlet with words of encouragement, urging him to continue his pursuit of excellence.

Three world records fell on this unforgettable night in Fukuoka.

Australia's Ariarne Titmus made a stunning comeback in the women's 400-meter freestyle, finishing with a breathtaking 3 minutes, 55.38 seconds, snatching back the world record from Canada's Summer McIntosh, who had wrested it from Titmus earlier in the year.

The highly anticipated showdown featured Titmus, Canadian record-holder McIntosh, and American defending world champion Katie Ledecky.

However, it was Titmus who dominated the race, leaving her rivals trailing in her wake.

"I honestly did not think about getting the world record back," Titmus humbly revealed after her triumphant swim. "I just wanted to come here and swim the way that I felt I was capable of swimming."

The clash between Titmus, Ledecky and McIntosh was a showdown of swimming titans, and Titmus' victory rekindled memories of her triumph at the Tokyo Olympics two years prior.

For Ledecky, the decorated 26-year-old, it was a valiant effort, as she aimed to add to her astonishing 19 world titles, already a record for women in swimming.

In addition to these breathtaking individual performances, Australia's relay teams were nothing short of remarkable.

The women's 4x100-meter freestyle relay team stormed to victory, rewriting history with a scorching world record time of 3:27.96, leaving the United States and China trailing in their wake.

The men's 4x100-meter freestyle relay also clinched gold, solidifying Australia's position as a swimming powerhouse.