China’s Sun Yang matched a feat previously achieved only by Australian Grant Hackett and American teenager Katie Ledecky became the second-fastest woman ever with victories in the men’s and women’s 400 metres freestyle at the world championships yesterday.

Sun, 22, the Olympic champion in London last year, equalled Hackett in claiming world titles at 400, 800 and 1,500 metres while 16-year-old Ledecky became only the second woman after Italian world record holder Federica Pellegrini to break four minutes.

The opening day of competition in the specially constructed pool at Barcelona’s hilltop Palau Sant Jordi was a triumph for the United States, who also took gold in the women’s 4x100 relay and silver in the men’s race behind France.

While Sun’s three titles in the longer freestyle events have come at two different championships – he won the 800 and 1,500 in Shanghai two years ago and was second in the 400 – he remains on course to repeat Hackett’s three golds from the 2005 edition in Montreal.

He led the 400 from the start yesterday, pulling inexorably away and touching in a time of three minutes 41.59 seconds.

Japanese teenager Kosuke Hagino took silver, more than three seconds behind Sun in 3:44.82, and American Connor Jaeger, 22, won the bronze in 3:44:85.

“In the last year I experienced many things and I still managed to win my gold medal,” Sun told reporters.

Ledecky, a gold medallist over 800 metres in London in the first major event of her career, leaped out of the water and punched the air after she secured the first US 400 freestyle gold since Janet Evans in 1991 and smashed the American record by nearly two seconds.

She was initially on course to break Pellegrini’s world best of 3:59.15 but slipped off the pace in the final 100 metres to finish in a time of 3:59.82.

Spain’s Melanie Costa Schmid gave the home supporters something to cheer by taking silver in 4:02.47 and Lauren Boyle of New Zealand was third in 4:03.89, the first woman to win a medal for her nation at a world championships.

The popular 4x100 freestyle relay events got the crowd on their feet.

Backed by a sizeable contingent, France from behind to see off the US, Russia and Australia.

France were fourth when Jeremy Stravius dived into the water for the final leg but he hauled in American James Feigen, Russia’s Danila Izotov and James Roberts of Australia to touch in three minutes 11.18 seconds.

The United States matched their silver from London in a time of 3:11.42 and Russia pipped Australia to the bronze in 3:11.44.

Megan Romano swam a blistering final leg to overhaul Australia’s tiring Alicia Coutts and snatch relay gold for the American women.

Australia led until the final 50 metres through Cate Campbell, her sister Bronte and Emma McKeon but Romano was too strong for Coutts.

Romano came home in 3:32.31, with the Australians finishing in 3:32.43 and the Netherlands were third in 3:35.77.

Chetcuti debut

Andrew Chetcuti made his first appearance in the world championships when he took part in the 50m butterfly heats.

The Maltese swimmer completed the one-lap race in 24.88 seconds, just 0.16 of a second slower than his personal best of 24.72 he clocked during last month’s Mediterranean Games in Mersin, Turkey.

In the overall standings, Chetcuti placed 42nd from an entry field of 80 swimmers.

Chetcuti will now be back in action on Wednesday when he takes part in the 100 metres freestyle heats.