KAZAN, Russia (AP) -- Competing in his first major event since his doping suspension was revealed, China's Sun Yang led the 400-meter freestyle heats Sunday as the traditional pool events at the swimming world championships opened.
Sun touched in 3 minutes, 44.99 seconds, winning his heat just an arm's length ahead of Britain's James Guy, who qualified second in 3:45.37.
After seeing his time, Sun gave a thumbs-up.
Ryan Cochrane of Canada was third in 3:45.86, while Australians Mack Horton and David McKeon failed to make the eight-man final, which was scheduled for later at the Kazan Arena, where a temporary pool has been set up inside a football stadium.
China's anti-doping agency revealed in November that Sun served a three-month ban earlier that year after testing positive for the banned stimulant trimetazidine.
Sun won the 400 free at the last two worlds plus the 2012 London Olympics.
Defending champion Katinka Hosszu of Hungary, nicknamed the "Iron Lady" for her success across multiple events, led the 200 individual medley heats in 2:07.30. Olympic champion Ye Shiwen of China was only fifth in 2:11.23.
Hosszu may swim up to seven individual events in the eight-day meet.
Sarah Sjoestrom, another defending champion, qualified first for the 100 butterfly semifinals in 56.47. Olympic champion Dana Vollmer is sitting out this competition, having only recently returned to competition after having a baby.
In a non-Olympic event, French sprinter Florent Manaudou was fastest in the 50 fly, with Hungarian veteran Laszlo Cseh second in 23.32.
"It's a big surprise for me. I feel I am very fast," Cseh said, adding that he has a new coach. "I have some motivation. It was a good decision for me. After that I start to enjoy it again."
Cesar Cielo of Brazil, the defending champion in the 50 fly only barely made the semis in 14th.
Finals in the women's 400 free and both men's and women's 4x100 free relays were also scheduled for later.