Singapore –

Leon Marchand and Summer McIntosh sealed their golden swimming world championships with dominant victories on Sunday's final day as the United States signed off with a relay record.

Eight days of competition in Singapore wrapped up with French superstar Marchand and 18-year-old Canadian sensation McIntosh underlining their supremacy.

Marchand, who won four individual golds and was the face of his home Paris Olympics a year ago, added the 400-meter individual medley crown to his 200 medley title this week.

The 23-year-old arrived in Singapore with a lighter program in an effort to smash Ryan Lochte's 200 IM world record from 2011 — and he did just that.

Marchand on Sunday cruised to victory in the 400 IM, powering to the wall in 4 minutes, 04.73 seconds, more than three seconds ahead of Tomoyuki Matsushita (4:08.32), with Russian Ilia Borodin, competing as a neutral athlete, third at 4:09.16.

Russian swimmers are competing as neutrals because of Moscow's invasion of Ukraine.

"It's not perfect because it's never perfect, but it's more than I expected, especially the world record in the 200-meter medley," Marchand said.

"It shows that I still have a passion for swimming, that I love it."

Not to be outdone, McIntosh was similarly emphatic in winning the women's 400 for her fourth gold in Singapore, to go with triumphs in the 200 medley, 200 butterfly and 400 freestyle.

The world record holder led from start to finish to romp to victory in a world championships-record 4:25.78, with Australia's Jenna Forrester and Mio Narita sharing silver (4:33.26).

McIntosh's only defeat of the championships came on Saturday when she finished third in the 800 freestyle, with American Katie Ledecky reigning over that event once more to underline her enduring quality at age 28.

"Overall happy with my meet but always wanting more," McIntosh said.

"Even if I were to get five golds, I would still want more, that's just my mentality."

The U.S. team battled acute gastroenteritis all week and faced flak from Olympic greats Michael Phelps and Lochte.

But they silenced the doubters by breaking their own world record in winning the women's 4x100 medley relay.

The Americans were victorious in 3:49.34, beating their previous record of 3:49.63 from Paris a year ago. They also set a mixed 4x100 freestyle world record on Saturday.

The U.S. ended a turbulent week on top of the pile with nine golds, ahead of Australia with eight and France and Canada on four — with all four Canadian golds coming from McIntosh.

American three-time Olympic gold medalist Bobby Finke called the criticism "weak" and "stupid."

"Someone wants to say our swimmers are entitled, that's just the dumbest thing I've personally ever heard," world record holder Finke said after winning bronze in the 1,500 freestyle.

China's 12-year-old schoolgirl Yu Zidi — whose presence at the championships at such a young age has ignited debate — was just out of the medals in fourth in the 400-meter medley.

Yu was fourth in all three of her individual events and looks set to become a superstar at the 2028 Los Angeles Olympics.

She goes home with a relay bronze from earlier in the week, and with it a slice of history as the youngest medalist ever.

Australia's Meg Harris beamed from ear to ear after joining compatriot Cam McEvoy as a 50 freestyle champion.

A day after McEvoy won the men's sprint, Paris Olympic silver medalist Harris powered home in 24.02 seconds to beat Chinese pair Wu Qingfeng (24.26) and Cheng Yujie (24.28).

Harris, 23, said becoming an individual world champion was "the dream I have been dreaming of the whole time."

Tunisia's Ahmed Jaouadi added the 1,500 freestyle world title to his 800 crown.

Jaouadi grabbed gold in 14 minutes, 34.41 seconds, ahead of Germany's Sven Schwarz (14:35.69) and Finke (14:36.60).

There was a Russian victory in the men's 50 backstroke, with Kliment Kolesnikov dominating for gold in a championships-record 23.68 seconds.

The Russians won the men's 4x100 medley relay over France and the United States.

Lithuania's Ruta Meilutyte sealed a career fourth women's 50 breaststroke world crown.