By Rod Gilmour
KAZAN, Russia (Reuters) - China's Sun Yang defended his men's 400 meters freestyle title at the world championships on Sunday, the first of a possible four-gold sweep for the 23-year-old.
Sun, the five-times world champion, clocked three minutes 42.58 seconds to take gold as the Chinese powerhouse overtook Britain's James Guy in the closing stages.
Guy, fifth at this event in Barcelona two years ago, was ahead until the 300m mark, before a surging turn opened up a lead which he never relinquished, winning by 1.17 seconds.
Sun will compete in three more individual events this week, the 200m, 800m and 1,500m freestyle.
Katie Ledecky, the brilliant 18-year-old who graduated from high school in June, had a far easier final to negotiate as the American coasted to gold in the women's 400m freestyle.
Like Sun, Ledecky is also competing in four individual races and she put down a marker for the week by setting a championship record time of 3:59.13, several seconds clear of her rivals.
Sharon van Rouwendaal, of the Netherlands, took silver.
Asked if she felt a lack of competition in her races, the defending champion said: "I think it's a very competitive event and I could feel the other girls racing really hard so that gets me going. It was a fast race.
"When I touched I kind of felt that I had it (a world record), so it took me a second to realize that. But at the same time I can't complain about another world championship medal."
Britain's Adam Peaty and Cameron van der Burgh twice traded championship records, suggesting that the men's 100m breaststroke final on Monday will be a thrilling affair.
Peaty first took the record in the morning heats, with 58.52 seconds, before Van der Burgh shaved 0.03 seconds off the mark.
In the semi-finals, Peaty set a new mark of 58.18 seconds.
Sweden's Sarah Sjostrom set the first world record of the eight-day meeting in the women's 100 meters butterfly.
Sjostrom's time of 55.74 seconds in the semi-final broke the previous record of 55.98 seconds set by Dana Vollmer, of the United States, at the London 2012 Olympics.
Australia won the women's 4x100m freestyle relay, with the Netherlands and the United States taking silver and bronze respectively.
France denied Russia in the final event of the night, the men's 4x100m freestyle relay.