Australian women win freestyle relay gold

Members of the Australian women's 4x100m freestyle relay team celebrate their gold medal performance. Al Bello/Getty Images

Australia's ruthless freestyle relay record-breakers should become the stuff of Olympic legend, jubilant swimmer Cate Campbell says.

Campbell, her sister Bronte, Emma McKeon and a 19-year-old on Olympic debut, Meg Harris, set a world record in winning Australia's first gold of the Tokyo Games.

Their 4x100m freestyle relay triumph came after a daring heist produced a silver medal for Jack McLoughlin in the men's 400m freestyle.

And unsung compatriot Brendon Smith pocketed a bronze in just his second Olympic swim, the 400m individual medley.

The relay world record extends Australia's golden run to three Olympics, a feat which demands respect, Campbell says.

"This is the third Olympics in a row that Australia has won this event and that in itself needs to be celebrated," she said.

"To do that for 12 years in a row is incredible."

Campbell has been on all three relay triumphs while teen sensation Harris travelled to Tokyo thinking she was just a heat swimmer.

"I was just so happy to swim in the heats. And the opportunity to do it again is insane, I'm just happy to be here," Harris said.

Their winning time of three minutes 29.69 seconds bettered Australia's previous world benchmark of 3:30.05 set at the 2018 Commonwealth Games.

Campbell iced victory with a power-laden final 100 metres but McKeon provided an ominous pointer toward the battle for the individual 100m freestyle crown

McKeon clocked a stunning 51.35, with her main rival Campbell's 52.24 an indicator to form entering the individual race.

"I'm feeling pretty good," the understated McKeon said.

"It has all worked out well and with the support of these girls you always feel you've got a bit extra."

Before swimming the relay final, McKeon cruised through a 100m butterfly semi-final amid a gruelling program featuring seven genuine medal shots.

In the men's 400m freestyle final, McLoughlin almost pulled off a brash victory after resolving on outright agression: set the pace, then hang on.

McLoughlin led until the final metre when outstretched by Tunisian surprise packet Ahmed Hafnaoui in lane eight.

"I just wanted to get out front and say 'chase me'. It almost paid off," McLoughlin said.

"I couldn't see all the way over (to lane eight) ... I knew they were coming at me and was just trying to get that hand on the wall."

In the 400m medley final, 21-year-old Smith operated in reverse to McLoughlin. He was last with 100m remaining before a flying freestyle leg delivered bronze.

"When the Games were postponed I knew it gave me an opportunity to be one year older and one year stronger," Smith said.

"It was a blessing for me but, saying that, I've gone through hell to be here.

"I've been swimming in the oceans for two months in Melbourne, getting down to 11-12 degrees in the water."