Jonny Brownlee finally made it to the top step of the podium with Great Britain winning the first mixed relay gold in Games history, beating home the US and France in a dominant performance.

For Brownlee, victory - in what is likely his last Olympic appearance - caps a brilliant Games career after bronze in 2012 and silver four years later in Rio in the men's individual event - which were won by older brother Alistair.

"It feels absolutely amazing to complete the set, to have three Olympic medals, three different colours," Brownlee said.

"A super, super amazing day and being part of the team and to win the first ever mixed team relay at the Olympic Games in triathlon, perfect day.

"... I'm pretty confident that'll be my last Olympic Games now, I'm ready for a different challenge now."

The British led for virtually the entire contest, first out of the water courtesy of Jess Learmoth in the opening leg, Brownlee handing women's individual silver medallist Georgia Taylor-Brown a lead and anchor leg Alex Yee holding off a strong challenge from the French to clinch gold.

Victory also confirmed Great Britain as the undisputed Olympic powerhouse in the sport.

They have now won eight medals from the past three Games - three gold, three silver and two bronze.

Their success is in stark contrast to the drop-off from the Australians, who for the first time in Olympic history did not make the top 10 in either individual race.

They entered the mixed relay with genuine medal hopes, having been podium regulars in the event.

But they faltered from the start and never recovered as they paid the price for a poor first transition, eventually finishing ninth after a strong anchor leg from Jake Birtwhistle dragged them back into the top 10 - some two minutes 46 seconds behind the Brits.

Emma Jeffcoat in the lead-off produced a tremendous swim to be third out of the water behind noted swimmer Learmoth, but was fifth out of the transition area onto the bike - 26 seconds behind the lead group of Great Britain, German, the US and the Netherlands.

That proved crucial, Australia regularly dropping time to the lead pack as first Mathew Hauser and then Ashleigh Gentle took to the course before Birtwhistle made up some time.

"This is obviously pretty disappointing - that's sport I guess, there's ups and there's down and unfortunately there are usually more downs than there are ups," Birtwhistle told the Seven Network.

"We'll regroup ... we know we are a great team, we deserve to be much higher up there in the results, we're all capable of that, today we'll put it past us and get on with the next one."

But the Tokyo disappointments continue a sustained downward spiral for Australia from the heady days of four medals - including Emma Snowsill's gold in Beijing in 2008 - from triathlon's first three Olympics.

Erin Densham's London bronze is Australia's most recent medal at the Games.

"Over analysis leads to paralysis," posted Australian Sydney 2000 competitor and now triathlon coach Craig Walton on Facebook.

"Time to get back to the basics Triathlon Australia."

Australian Associated Press