Sydney McLaughlin-Levrone teased the possibility of running an extraordinary 400 metre double at her home 2028 Olympics after a sizzling world gold in the flat race Thursday silenced the doubters.

The 26-year-old American is the world record holder and two-time Olympic gold medallist in the 400m hurdles but chose to run the flat race at the world championships in Tokyo.

Her decision was emphatically vindicated after clocking the second-fastest time ever, winning in a championship-record 47.78sec.

McLaughlin-Levrone will be on home soil at the 2028 Los Angeles Games and is not ruling out competing in a 400m double bill.

"We will need to talk about the schedule for the Los Angeles 2028 Olympic Games -- maybe I could do both 400m and 400m hurdles," she said.

"I would need some days off between those events and there is a tough field in both events. You've got to respect all the girls.

"In order to put your best performances together, you need your body to be ready for it," she added.

McLaughlin-Levrone fended off defending champion and Olympic gold medallist Marileidy Paulino of the Dominican Republic to take gold on a rain-slicked Tokyo track.

Her time smashed the previous championship record of 47.99sec set by Jarmila Kratochvilova of then-Czechoslovakia in 1983.

Some had questioned the wisdom of her decision to step away from the 400m hurdles, an event in which she went unbeaten for six seasons.

- Answering the critics -

She answered her critics in imperious fashion, two days after smashing the US record in the semi-final.

"I know there was a lot of doubt from a lot of people for me making this switch and I just wanted to show myself I can do it," said McLaughlin-Levrone.

"I see things online. I see what people say and ultimately, that's okay. I think that's what makes the sport great. I think they want to see great matchups.

"They want to see people be uncomfortable and I think today was a really great race for track and field."

McLaughlin-Levrone was drawn in lane five and made a powerful start in steady rain at Tokyo's National Stadium.

She put herself in front heading into the final straight although Paulino briefly looked like she might threaten from the outside lane.

Instead McLaughlin-Levrone propelled herself over the line first, falling agonisingly short of the world record of 47.60sec set by Marita Koch of then-East Germany in 1985, one of the oldest records in the books.

She was left gasping for air and took a moment to compose herself before returning to the track and celebrating with her husband Andre.

The new champion said she "knew this feeling was going to be amazing".

"It definitely helped having Marileidy Paulino in the outer lane where I could see her, but I still had to get the work done," said McLaughlin-Levrone.

"My coach told me to get out of the blocks as fast as possible, not to stay in it for long.

"I knew the girls were going to push me but what mattered was to stay composed," she added.