The host country has now won eight gold medals after the heavyweight duo stormed to victory in Melbourne on Thursday night while Chalmers also anchored the men’s 4x50m freestyle team to a last-gasp win.

Australia only trails Team USA in the medal tally by one gold medal.

Despite owning 17 Olympic medals between them, neither McKeon nor Chalmers had previously won an individual world championship title at either short or long course.

But McKeon blitzed the women’s final with Siobhan Haughey from Hong Kong second and Dutch swimmer Marrit Steenbergen collecting the bronze medal.

Fellow Australian Madi Wilson was fourth.

With her former pop star boyfriend Cody Simpson watching on, McKeon stopped the clock in 50.77 seconds, touching 0.10 ahead of defending champion Haughey.

“It was a tight finish – I only just realised after the race but to get my hand on the wall first is all you really want,” McKeon said.

The reigning 50 and 100m Olympic champion, McKeon signalled her intentions with a blistering relay leg on Tuesday night which helped Australia win gold in the 4x100m freestyle relay in world record time.

World record holder Chalmers motored home in the final lap of the men’s 100m freestyle final to reel in leader Jordan Crooks from the Cayman Islands, who faded from the medal positions.

Chalmers touched the wall in 45.16 – outside his world best time of 44.84 – with Frenchman Maxime Grousset second in 45.41 and Italian Alessandro Miressi taking bronze in 45.57.

The long course world record holder, Romanian teenager David Popovici, was fourth.

“I had to pull out of the last three world short course championships due to injury and health issues so for me to finally make it to one and stand on the top of the podium is something I’m going to remember for the rest of my rest of my life,” 24-year-old Chalmers said.

While the Australian women, with McKeon on board, had to settle for silver in their 4x50m freestyle relay behind the USA, Chalmers grabbed gold in the men’s relay with a powerhouse final lap to pip the Italians by just 0.04.

Isaac Cooper led the Australian team out with Matt Temple and Flynn Southam following before Chalmers hit the water in fifth spot.

But the speed king mowed down the field with a split of 20.34.

Australia won two other medals on day three with 20-year-old Thomas Neill surprising to win silver in the men’s 400m freestyle behind American Keiran Smith while fellow young Queenslander Lizzie Dekkers trailed American Dakota Luther to claim bronze in the 200m butterfly.

As well as his relay gold Cooper, who won bronze in the 100m backstroke, shocked the 50m backstroke field and will go into the final as the fastest qualifier.

The 18-year-old was banished from the Commonwealth Games team for misusing prescription medication but has bounced back in style.

“It was really tough today as the fatigue is really setting in and in the warm-up pool I felt horrible,” the Queenslander said.

“I’ve known I’ve had that speed for a while and I’m glad I could execute.”

In other results, South African Chad Le Clos won the men’s 200m butterfly, American long course world record holder Lilly King clinched gold in the 100m breaststroke and teammate Nic Fink took out the men’s equivalent.

-AAP