Kazan (Russia) (AFP) - China's superstar Sun Yang successfully defended his 400m freestyle title with gold in Sunday's final as he opened his world swimming championship campaign in style.The Olympic champion clocked three mins 42.58 seconds with Britain's James Guy taking silver at 1.17secs back and Canada's Ryan Cochrane won bronze at 2.01 secs as the first medals of these championships were decided in Kazan.This is the first of four individual events Sun, the world 1500m freestyle record holder, will race in Kazan as well as the 200m, 800m and the mile distance. He courted controversy in 2014 after it emerged he had served a three-month doping ban from the Chinese swimming authorities for taking a banned stimulant.Having won the 400m and 1500m freestyle Olympic titles at the 2012 London Olympic Games, Sun continued his domination of the endurance events by winning the 400m, 800m and 1500m world titles in Barcelona two years ago. Join the conversation about this story »