Swimming champ reveals the baffling decision that cost Australia an Olympic gold medal in the women's 4x200m freestyle relay in Tokyo

Australian Olympic great James Magnussen has hit out at a series of selection blunders that led to the Golden Girls being stunned by China and the USA in the women's 4x200m freestyle final. 

Ariarne Titmus swam the first leg for Australia followed by sprint specialist Emma McKeon, Madison Wilson and Leah Neale as the Dolphins claimed only bronze from a race some bookmakers had them as extraordinary $1.04 favourites to win.

None of Australia's final line-up had featured in the heat. 

The move not to finish with Titmus, who has already won two gold medals at the Tokyo games, drew eyebrows from swimming legend Ian Thorpe before the race.

Magnussen, a world champion and three-time Olympic medallist, meanwhile said Australia would likely have won at least a silver medal had 17-year-old Molly O'Callaghan started in place of Neale.

Australia were stunned in the final of the women's 4x200m freestyle with China and the USA hunting down the strong favourites and the country's Golden Girls. Pictured Australia's bronze-medal winning lineup of Ariarne Titmus, Emma McKeon and Madison Wilson after Leah Neale finished in third

Australia's 4x200m women's team with their bronze medals after the race. James Magnussen, an Australian world champion and a three-time Olympic medallist, said the Dolphins would likely have won at least a silver medal had 17-year-old Molly O'Callaghan started in place of Neale

While the race was Neale's first and only scheduled swim at the games, O'Callaghan had posted the 18th fastest time in history in the 4x200m heat.

'You can understand why Mollie’s parents were lost for words when informed Mollie would not be in the finals team,' Magnussen wrote in a column for News Corp.

He argued if the teenager had swum her final leg in the same time she did during the heat - a world junior record of 1.55.11 - the girls would have at least pipped the US to second place.

Allowing for a relay changeover, Australia would have lived up to their billing and claimed gold from China.

O'Callaghan posted the 18th fastest time in history in the 4x200m heat but was left out of the final by selectors

He said the four fastest 200m freestyle times from Australia's swimmers (Ariarne Titmus, Emma McKeown, Mollie O'Callaghan, Madison Wilson) equaled 7:38.62 -  almost two seconds quicker then China's eventual winning time of 7.40.33.

'Up until today the coaching staff have nailed every relay selection and order,' Magnussen said. 'On Thursday, however, the team made its first major blunder.'

'Put simply, the wrong team took the blocks in the final.' 

He said a bronze medal in a games was an outstanding achievement but short of expectations for an Australian women's swimming team filled with so much talent.

Ex-Olympic gold medallist Giaan Rooney echoed Magnussen's sentiment, saying it was a 'big miss' to have O'Callaghan out of the team.

'I don't know for sure but I think the idea was for both Titmus & McKeon to swim fast but 'comfortably' up front (they both have individual events left) and to have enough of a lead after Wilson for Neale to anchor - biggest miss was Mollie O - 1.55.10 in the heat,' she tweeted following the race.

'Would love to know the thought process behind it.' 

Aussie swimming legend Ian Thorpe said he was confused with the team's lineup just before the race as Titmus stepped up to the blocks 

Despite Australia starting with its best swimmer it was China - who were $41 outsiders before the heats - that led after the first change. 

McKeon took over from the 20-year-old Tasmanian and within the first 50m had overtaken her Chinese opponent, but China snatched back its lead at the halfway mark with both teams well ahead of world record time. 

Wilson handed over to Neale for the final change as American swimming star Katie Ledecky tried to catch up to China.

Neale couldn't overcome the Chinese and Americans, leaving the Aussies devastated behind the blocks, left to reflect on what went wrong.

Ledecky posted a lightning fast final 200m to push China all the way to the wall.  

Despite Australia leading with their best swimmer, Ariarne Titmus, China led after the first change and all the way until the finish

The decision to completely overhaul the relay team from heat to final, and lead with their best two swimmers, will be severely scrutinised as it appears Aus have thrown away a gold medal

Australia was a red-hot favourite for the event with the individual gold medallist Titmus and sprint queen McKeon in the ranks but was never in control of the race.  

The foursome finished with a time of 7:41.29, faster than their heat time of 7:44.61.  

Titmus, who has been the star of the Games so far for Australia, added a bronze to her two golds but lost an opportunity to become just the eighth Aussie to win three golds at one Olympics.

She will face-off with Ledecky one more time in the 800m freestyle. 

Kyle Chalmers, who touched in an agonising 0.06 seconds behind USA's Caeleb Dressel in the 100m freestyle less than an hour before their relay, was supporting the relay team from the stands. 

 Kyle Chalmers, who touched in an agonising 0.06 seconds behind USA's Caeleb Dressel in the 100m freestyle less than an hour before their relay was supporting from the stands

Aussie sprint king Kyle Chalmers has finished second in the final of the 100m freestyle with America's Kyle Dressel taking gold 

Earlier, the Aussie sprint king touched the wall a fingernail behind Dressel to finish second in the final of the 100m freestyle.

Chalmers, who came from nowhere to win gold as an 18-year-old at the 2016 Rio Olympics, was looking to become the first Aussie to repeat as the fastest man in water.

Chalmers said he was re-watching his 100m freestyle win at the 2016 Olympics this morning in the lead up to the race for inspiration as he attempted to pull off the historic achievement. 

The Aussies have continued to dominate in the pool with Zac Stubblety-Cook winning gold at the 200m breastroke final on Thursday

The 23-year-old from Port Lincoln touched in behind the USA's world champion for Australia's second silver medal at the Tokyo Games.  

'Winning isn't everything… but it's pretty nice,' the devastated swimmer said post race. 

'If the Games were last year, I wouldn't be here.

'I'm grateful for the support, my family and friends who have been there since day one. They've always been there for me.' 

Australia's Zac Stubblety-Cook has won gold and broken an Olympic record in the men's 200m breaststroke final at the Tokyo Games

Zac Stubblety-Cook won gold and broke an Olympic record in the men's 200m breaststroke final earlier  on Thursday.

The 22-year-old from Queensland touched the wall in record time at 2:06.38 followed closely behind the Netherlands' Arno Kamminga and Finnish swimmer Matti Mattsson.

Stubblety-Cook had been a favourite to win after taking out first place in the semis with the fastest time of 2:07.35.

It was the first time an Australian had won the 200m breaststroke final at the Olympics since the previous Games in Tokyo in 1964.

Stubblety-Cook's family and long-term girlfriend Ella Martinkovic cheered him on from home.

'Unbelievable, without their support I wouldn't be here but it's been a tough five years,' he said.