KAZAN, Russia (AFP) - China's swimming superstar Sun Yang got his world championship campaign off to an impressive start as he posted the fastest time to ease through to Sunday night's 400m freestyle final in Kazan.
The 23-year-old, the event's reigning world and Olympic champion, clocked 3min 44.99sec as Britain's James Guy, Canada's Ryan Cochrane and world bronze medallist Connor Jaeger of the United States also booked their berths.
The Chinese giant dominated the long-distance freestyle events in Barcelona two years ago with world titles in the 400m, 800m and 1500m.
World record holder Katie Ledecky of the US was the fastest qualifier into Sunday night's 400m freestyle final just ahead of Australia's Jessica Ashwood, with New Zealand's Lauren Boyle, the world bronze medallist from two years ago, the fourth fastest through.
There was a massive shock in the men's 4x100m freestyle relay heats with both the US and Australia, along with Britain and Germany, failing to qualify for the final, as reigning Olympic and world champions France went through in the second-fastest time behind Russia (3:12.46).
It was the first time the US had failed to make the final at a world championships.
Singapore's Quah Zheng Wen, Danny Yeo, Pang Sheng Jun and Lionel Khoo were 28th out of 30 teams in a slow 3:27.01.
The US women's team had no such problems and rested stars Ledecky and Missy Franklin, but were still the fastest through to the final, closely followed by Australia and the Netherlands.
Sun courted controversy last year after it emerged he had served a three-month doping ban from the Chinese swimming authorities for taking a banned stimulant.
He will be defending his three titles in Kazan, plus racing in the 200m in what promises to be a busy schedule.
There was disappointment for Australian teenager Mack Horton, as the 2015 world leader in the event finished 11th in the 400m heats to miss the final by 18 hundredths of a second.
"It was my first international meet and I wasn't really sure of the pace, it took me by surprise, but there's still a long way to go in the meet" said the dejected 19-year-old, who also goes in the 800 and 1,500m freestyle events.
Britain's double world record-holder Adam Peaty set a new championship record of 58.52sec on his debut in the heats to reach Sunday evening's 100m breaststroke semi-finals.
"That was my first world championships and the crowd out there was more like what you'd get for finals, it was mad," said the 20-year-old, who has broken the 50m and 100m breaststroke world records in the last year.
"I was a bit more nervous than usual, but I'm well set up now for the semis."
Olympic champion Cameron van der Burgh of South Africa was the second fastest through, but there was a shock for reigning champion Christian Sprenger of Australia, who finished 28th and failed to make the semis.
"It was slow, very slow," said a disappointed Sprenger. "I was OK in the warm-up, but it just didn't click."
South Africa's 100m butterfly world champion Chad le Clos opened his Kazan campaign by comfortably qualifying for the men's 50m semi-finals as eighth fastest behind France's Laurent Manadou and Hungary's Laszlo Cech, who were the fastest through.
"I feel good, I'm happy with the time and I'm in the best shape I have been in for a while," said the 23-year-old Olympic, world and Commonwealth 200m champion.
Le Clos has a busy campaign in Kazan and will race in the 100 and 200m fly, the 200m freestyle and 200 individual medley.
Hungary's "Iron Lady" Katinka Hosszu set a new European record of 2:07.30 in the 200m IM heats, as the reigning world champion blasted her way into Sunday evening's semi-finals.
"I broke my own European record and I am looking forward to coming back and going faster in the semis," said the 200m and 400m IM world champion.
China's Ye Shiwen, the Olympic champion, showed no signs of a reported ankle injury as she booked her semi-final berth as the fifth-fastest qualifier.