(Reuters) - American Katie Ledecky can become the most successful female Olympian of all time with another golden haul in Tokyo but Australia's Ariarne Titmus could be the dasher of dreams.
The duel in the pool between Stanford University graduate Ledecky, the dominator of women's distance swimming, and 20-year-old Tasmanian "Terminator" Titmus promises to be a highlight of week one.
Ledecky has four golds and a silver from the Rio 2016 Games, on top of the 800m freestyle gold she won as a 15-year-old at London 2012.
Three more golds would lift the 24-year-old alongside retired compatriot Jenny Thompson as the most successful female Olympic swimmer with eight.
Five more golds, not out of the question with Ledecky qualifying in four individual events -- the 200, 400, 800 and 1,500 freestyle -- and relays on top, would be a record for any female athlete.
Ledecky holds the world records in 400, 800 and 1,500 free, with the latter a new addition to the women's programme, and another 800m gold would be her third in a row in the distance.
Only three swimmers, one of them retired U.S. great Michael Phelps, have pulled off such a hat-trick.
Titmus, however, can see a different storyline.
She caused a sensation at the 2019 world championships when she beat an unwell Ledecky to the 400m gold, and the Tasmanian destroyed the opposition in the 200, 400 and 800m freestyle Australian qualifiers in Adelaide in June.
"She’s not going to have it all her own way I guess," said Titmus after clocking the second fastest 400m time ever and promising to leave everything in the Tokyo pool.
"I can’t control what she does, I can only control myself and if I do the best I can and put myself in that position to win a gold medal, it is going to be some race."
Australia's excitement was fuelled further by newcomer Kaylee McKeown breaking American Regan Smith's 100m backstroke world record on day two of the national trials.
"I think the Olympics are not going to be all America’s way," said Titmus.
The United States topped the swimming table in Rio with 33 medals, including 16 golds. Australia came second, with 10 and three golds.
Sweden's Sarah Sjostrom, the 100m butterfly Olympic champion, has made it to Tokyo after breaking her elbow in February.
Hungary's Katinka Hosszu, who won three golds in Rio, is aiming to defend her 400 individual medley title and Canada's Penny Oleksiak her 100m free title.
On the men's side, Caeleb Dressel is targeting a haul of gold in the first Summer Games in a quarter of a century without compatriot Phelps.
Phelps, winner of a record 28 career Olympic medals including 23 golds, is in Tokyo as a television pundit only.
Dressel won two relay golds in Rio but his eight medals at the 2019 world championships sent hopes soaring and he remains the favourite in the 50 and 100m freestyle as well as 100m butterfly.
At a Games where the COVID-19 pandemic has disrupted training for many, there is a question mark over how many records might be broken.
Expect Britain's reigning champion and world record holder Adam Peaty to try and beat his 56.88 benchmark in the 100m breaststroke.
"We've done the sums and I think if it went absolutely perfectly, and I’m talking the fastest parts that I’ve done in a physical race and you put them all together, it’s 56.2 or 56.3 which is absolutely ridiculous," he said.
"I’m not saying I’m going to go that...but I do believe I can get faster than the world record."
Hungarian Kristof Milak is another to watch after taking possession of Phelps' 10-year 200m butterfly world record.
(Writing by Alan Baldwin, editing by Ed Osmond)