China's Sun Yang ticked the first box on the way to a possible treble of freestyle golds when he comfortably won the 400 metres at the world swimming championships on Sunday.

The 22-year-old, who was Olympic champion in London last year, led from the start to improve on his silver medal from Shanghai two years ago with a time of three minutes 41.59 seconds.

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

Sun, who also won the 1,500m gold in London, is bidding to join Australia's Grant Hackett as the only men to win world championship freestyle titles at 400m, 800m and 1,500m.

Photograph: Al Bello/Getty Images