RIO DE JANEIRO • All eyes will once again be on Michael Phelps as he leads the mighty United States into battle in the Olympic swimming competition, where traditional rivals Australia lie in wait to cause a few upsets.
Phelps, whose record 22 Olympic medals include 18 golds, caps his career with a fifth Games appearance in Rio. The American could feature in tomorrow's 4x100m freestyle relay final where he could add to his gold-medal tally.
But, just as he is far from invulnerable at 31, the United States, whose men have not failed to finish in the top three since the event was introduced in 1964, could find themselves hard-pressed to match their 2012 haul of 16 golds, nine silvers and six bronzes.
Australia are aiming to rebound from a shocking 2012 London Games - their first since 1976 without an individual gold.
Australian coach Jacco Verhaeren, however, said the 2016 squad's mission has nothing to do with atonement.
"I don't think we're here to make up for any disappointment," he said. "Nobody is busy with what happened or what might happen."
Australia's Cate Campbell is on a high after breaking the long-standing women's 100m freestyle world record in July, while Cameron McEvoy is a title contender in the men's 50m and 100m freestyle.
"It's always special to stand up against the Americans," said McEvoy. "That mutual respect gets the adrenaline pumping."
But swimmers from around the globe are set to challenge the twin powerhouses when the eight-day competition kicks off today.
"I think this sport has changed to where there's not really one or two powerhouses," said Phelps.
"The Australians have made a significant charge over the last couple of years. There are a lot of young guys who have really stepped up."
China will be keen to at least maintain the second place in the swimming medal table which they achieved for the first time in London with five golds.
Sun Yang, looking to defend his 400m and 1,500m freestyle gold medals in 2012, heads a Chinese squad that also includes Ning Zetao, 2015 world champion in the men's 100m free, and Ye Shiwen, reigning champion and world record holder in the women's 400m individual medley.
Kosuke Hagino leads the Japanese charge. He is aiming to wrest the 400m individual medley gold from American hands.
South Africa's Chad le Clos - who beat Phelps in the 200m butterfly in London - is back to try to hold off the American bent on revenge.
Hungarian Laszlo Cseh tops the world rankings in the 100m butterfly - one of two events Phelps is trying to win for a fourth straight time.
NOT JUST USA AND AUSTRALIA
I think this sport has changed to where there's not really one or two powerhouses.
Australia's women are an imposing bunch, but the US have a one-woman wrecking crew in Katie Ledecky.
Still just 19, Ledecky has gone from strength to strength since her surprise 800m freestyle triumph in London.
The women's 4x100m freestyle is today's highlight and Ledecky is tipped to swim in the preliminary heats to qualify for a medal in an event world champions Australia are favourites to win.
"The first two nights of the relays, with the women's on the first night and the men's on the second, there will probably be a lot of fireworks," said Phelps.
AGENCE FRANCE-PRESSE, REUTERS