Sydney (AFP) - World champion Mollie O'Callaghan was untouchable in the 100-metre freestyle and Emma McKeon too hot over the 100-metre butterfly, but it was not enough to prevent the United States edging Australia to claim another "Duel in the Pool" crown on Sunday.
Teenager O'Callaghan burst on to the scene this year, taking both the world and Commonwealth 100-metre titles among a flurry of medals, and she comfortably won again at the Sydney Aquatic Centre.
The 18-year-old hit the wall in 54.01 seconds ahead of Madi Wilson on the third and final day of a competition centred around traditional sprint events but also never-seen-before formats with points accumulated across individual and relay races.
"After (the) Commonwealth Games it was hard to get motivated again and train, but the support from everyone on the team has been amazing and I'm really enjoying (the meet)," said O'Callaghan.
The United States went into the final day leading by 13 points and ultimately won the competition 309-283 to keep intact their unbeaten record spanning 19 years and eight Duel in the Pool events.
The event initially took place every two years from 2003 to 2015, with the first three meets against Australia and the next four against Europe.
It underwent a revamp to broaden its appeal for its return, with regular racing joined by other quirky formats designed to add fun and excitement, where unique point bonuses were earned and strategy was crucial.
They included "mystery" medley races in which the order of strokes was randomly determined at the start, meaning some started off the blocks swimming butterfly, while others began with breaststroke, freestyle or even backstroke.
There were also "broken" 400-metre and 800-metre freestyles, where swimmers stopped at certain distances to earn points.
The 400-metre free had a 200-metre race, followed by a pair of 100-metre races off the blocks after a brief break, with points awarded to the winner of each.
The meet included a mixed 4x50-metre relay featuring disabled and non-disabled swimmers, the first time such an event has ever been held, as the sport looks to further integrate Para athletes.The US took the inaugural honours.
Among the regular events, McKeon was always in charge in the 100-metre butterfly, touching more than a second ahead of American Gabi Albiero in 57.05.
"I like knowing there's extra pressure, it makes me race harder," said Olympic star McKeon, who also contested the relay with Para athletes.
"I definitely like the newer races, the able-bodied and Para one was the first time it's ever been done and so good to be part of."
A strong US team claimed a thrilling men's 4x100-metre freestyle relay in 3:14.15 while American world 50-metre backstroke champion Justin Ress took the 100-metre title in 53.12.
American teenager Luke Hobson outpaced teammate Trenton Julian to touch in 1:45.59 and win the 200-metre freestyle, fulfilling a season ambition.
"I told myself earlier this year I wanted to do a 1:45 and I got it here," said the fast-improving Hobson.
David Curtiss won the men's 50-metre freestyle for the USA in 21.84 while Australia's Chelsea Hodges claimed the women's 100-metre breaststroke in 1:06.90.
