China's Sun Yang destroyed the field to win a hat-trick of men's 400 metres freestyle titles while American Katie Ledecky reached more milestones in her glittering career as the swimming got underway at the world aquatics championships on Sunday.

Sun posted a world-leading time of three minutes 41.38 seconds as he eased to victory by more than a body length over bitter Australian rival Mack Horton.

Horton beat Sun to the Olympic title last year in Rio de Janeiro, with the Australian calling the Chinese a "drug cheat" before the Games in reference to Sun having served a three-month ban in 2014 after testing positive for a banned stimulant.

Sun said at the time that the stimulant was in medication to treat a heart issue and did not enhance his performance.

In a race billed as 'War on the Water, Part 11', the rivalry in the pool failed to materialise on Sunday as Sun become only the second swimmer to win a third 400 freestyle world title after Ian Thorpe of Australia 14 years ago.

The 25-year-old Sun, wearing a distinctive pink swimsuit, looked in ominous form after taking the lead at the 150m mark and, after garnering his eighth world title, he glared at Horton who was racing in lane two after a sluggish morning heat.

The Australian had to settle for silver, 2.47 seconds behind, with Gabrielle Detti of Italy taking bronze.

Thirty minutes later, Ledecky duly bagged the 400m freestyle in another one-woman show of speed and agility.

The 20-year-old college swimmer's championship record time of 3:58.34 secured a trio of world titles as she became the first woman to do so in any discipline.

Leah Smith ensured a United States one-two, while Li Bingjie of China touched for bronze.

Ledecky also helped the US to a brilliant gold in the women's 4x100m relay - which included a world record for Swede Sarah Sjostrom for the 100m freestyle - as the American quartet ruined Olympic champions Australia's title defence.

Leading off the Swedes, who finished fifth, Sjostrom posted 51.71 seconds, smashing the time set by Australian Cate Campbell last year by 0.35 of a second.

Katinka Hosszu is favourite to follow Ledecky into the record books, judging by her form in the 200m individual medley semifinals.

The Hungarian, roared on by 12,000 fans inside the Duna Arena, qualified fastest for Monday's final in a time of 2:07.14.

Adam Peaty of Britain showed that he has the potential to lower his world record mark of 57.13 seconds after easing into the men's 100m breaststroke final.

A frenetic end to the evening's action saw the US regain top honours in the men's 4x100m freestyle relay.

The quartet of Calaeb Remel Dressel, Townley Haas, Blake Pieroni and Nathan Adrian edged Brazil into second place.

"The French are not here, as a long-term opponent of us, but we have the Brazilians as a new one," said Adrian.

Source: Khaleej Times