Roundup: Sun Yang and Ledecky win in Kazan worlds, Sjostrom rewrites women's 100m fly WR

China's swimming superstar Sun Yang and American teenager Katie Ledecky both made a good start at the Kazan world championships here on Sunday, while Sweden's Sarah Sjostrom renewed the women's 100m butterfly world record in the semifinal.

Sun, London Olympic champion of the men's 400-meter freestyle, claimed his third straight 400m free world title with a 3:42.58 finish.

The 23-year-old Sun trailed British swimmer James Guy in the first 300 meters. He managed to surpass Guy before the 350 meters and win the final. Guy trailed in 3:43.75, and Canada' s Ryan Cochrane came third in 3:44.59.

"It' s a difficult race," said Sun, who won the 400m, 800m and 1,500m freestyle at the 2013 Barcelona worlds. "The British swimmer was a big threat. I put all my effort in the last 100m. I think the competition in next year' s Olympic Games will be more fierce."

Sun was happy with his winning time, though it was much slower than his personal best 3:40.14 which was produced at the London Games.

"It is my best result after 2013," said the winner. "It means I am in a good form recently. I hope I can renew the world record of the event at Rio."

Sun will also take part in the 200m, 800m and 1,500m freestyle in Kazan.

Ledecky, 18, timed 3:59.13 to make a new competition record and win the first swimming gold for the United States at Kazan. Sharon Van Rouwendaal of the Netherlands finished second in 4:03.02, while Jessica Ashwood from Australia came third in 4:03.34.

Ledecky's events in Kazan are the same with Sun. She will also compete in 200m, 800m and 1,500m free.

In the women's 100m fly semis, Sjostrom of Sweden touched in 55.74, 0.24 seconds faster than the old WR of 55.98 produced by American Dana Vollmer at London Games.

One thing stunned the world on Sunday' s pool was that the United States failed to make the men' s 4x100m freestyle relay. The American men have won the 4x100m free relay for 11 times in 15 previous worlds. The only other time they didn't make the final was back in 2001 in Fukuoka, Japan.

France won the relay gold in 3:10.74, followed by Russia in 3:11.19 and Italy in 3:12.53 respectively.

China made a history by making the final of the event, and made a seventh finish with 3:15.41.

Australia won the women's 4x100m freestyle relay in a world championships record 3:31.48, followed by the Netherlands and the United States in 3:33.67 and 3:34.61 respectively.

China's Lu Ying made the final of the women's 100m butterfly and Olympic champion Ye Shiwen also reached the final of the women's 200m individual medley. Endi