The 20-year-old never appeared out of place in the race - while Ariarne Titmus remained unbeatable in the distance, Fairweather closed strongly and could have overhauled Katie Ledecky with few extra metres of water.
But the reaction of the medallists both in the pool and out suggested she was, to them, merely another minor-place finisher.
That reflection was unfair to Fairweather. Only five women in history have broken four minutes in the 400 free: Fairweather, the three swimmers ahead of her, and one since retired.
Yet this event always looked to follow international prognostications, the three medallists pre-ordained with only the order to determine.
Canadian Summer McIntosh was the sole finalist capable of keeping to Titmus’ imperious pace. Immediately after touching first, the Australian embraced her 17-year-old rival, likely knowing that one day McIntosh would usurp her the way Titmus once did to Ledecky.
The legendary American, having claimed her first Olympic bronze to sit alongside seven gold and three silver, soon joined the pair. Fairweather faced her pain in solitude.
Tears flowed once she exited the pool, a time of 4m 1.12s more than a second short of her personal best, though a smile had been restored once she spoke to a small contingent of media.
“I’m a bit gutted to get fourth, nobody wants to be there,” Fairweather said. “I might be a little bit upset now but I can definitely see the bright side of it already.
“Being among all those girls is awesome. I’m in one of the most competitive races there is so I can’t complain.”
Ledecky would voice a similar sentiment, but actions were less persuasive when assessing her satisfaction with third. Much to the chagrin of the waiting American press pack, the 27-year-old ignored typical post-race commitments, laying low in the comfortable confines of the warm-down pool.
When she did speak, following the medal ceremony, Fairweather was the furthest thing from her mind.
“Competing against the best in the world is something special and something we enjoy, especially since we’re the top three performers in that event,” Ledecky said.
“We have a lot of respect for each other and we love competing with each other. It brings the best out of us and I’m sure it pushes each of us in training, knowing we have each other to race.”
Titmus, who became the first swimmer in 100 years to defend her title in this event, said the additional impetus provided by such relentless competition came also with greater burden.
“I probably felt the expectation and pressure of this race more than anything in my life, to be honest, and I’m pretty good at handling the pressure. But I definitely felt it.”
This showdown was 20 years after another Australian won the original Race of the Century, Ian Thorpe triumphing in a 200 free field of eight men who combined for 34 Olympic and 58 world championship titles over their careers.
Thorpe, a five-time gold medallist, told the Herald that being able to balance the pressure was part of what made Titmus, known as the Terminator, so unstoppable.
“To know that this is the race the world is watching, it adds another level of complexity,” he said. “You’re at the point where you’re peaking, your anxiety is going through the roof, and if that gets to a point where it’s too much, you’re done. You’re cooked.”
There was no sign of angst in Fairweather as she was introduced, joining her Antipodean foe in greeting the 15,000-strong crowd with a smile and a wave, while the North Americans offered nothing behind dark goggles.
Fairweather later said she could hear a group of 10 teammates sitting at the opposite end of the pool, just beyond the waiting podium, a place no New Zealand swimmer has stood since Danyon Loader took double gold at Atlanta in 1996.
As the crowd was issued instructions to quiet, the finalists assumed their positions beside the blocks. Fairweather, in lane three, looked across the pool. Immediately in front was Ledecky’s back; beyond, the eventual gold and silver medallists, facing each other.
Three athletes who will be remembered among the greatest to wear a swim cap. A young Kiwi who could only watch.
Kris Shannon has been a sport journalist since 2011 and covers a variety of codes for the Herald.