China's Sun Yang proved he has few peers in the distance freestyle events on Sunday, while US star Missy Franklin claimed the first of what could be eight golds at swimming's world championships.
China's Sun Yang celebrates after winning the final of the men's 400-metre freestyle swimming event in the FINA World Championships at Palau Sant Jordi in Barcelona on July 28, 2013.
The 21-year-old Sun won the world men's 400m freestyle gold to complete the set of major titles in the event, 12 months after winning the Olympic crown.
Just as he did in the London 2012 final, the 21-year-old Chinese dominated early on in Barcelona to add the 400m world title to the 800m and 1500m freestyle golds he won two years ago in Shanghai
"The 400m is a very important event and I completed my goal," said Sun, who has moved to Hong Kong in the wake of a fallout he had concerning his girlfriend, an air stewardess, with his previous coach.
"I overcame many problems and proved myself, I hope to have an even better performance in my other events," he said as he prepares to start the defence of his 800m freestyle title in Tuesday's heats.
Sun clocked 3min 41.59sec, finishing more than three seconds ahead of the field, to cap a bright start on the first of the eight-day long championships for China as Ye Shiwen eased into Monday's women's 200m individual medley final.
The 17-year-old Ye, who won 200 and 400m IM gold Olympic medals last year, sparked controversy when she swam the final leg of her 400m triumph in a faster time than men's winner Ryan Lochte at London 2012.
Defending champion Ye was the second quickest qualifier, just over half a second behind Hungary's Katinka Hosszu, the fastest out of Sunday's 200m IM semi-finals.
The USA claimed two world titles on Sunday as 16-year-old Katie Ledecky just missed the women's 400m freestyle world record on her way to winning gold, finishing more than two and a half seconds ahead of her rivals.
The teenager, who enjoyed a shock win in the women's 800m freestyle at the Olympics, just missed out on breaking the four-year-old world record.
"I really wasn't expecting to go that fast, that wasn't my focus. I just wanted to compete with these girls and get the gold medal," said Ledecky, who will also race in the 800 and 1500m.
The Americans kept on a role as Franklin swam the first leg to lead the USA to the women's 4x100m freestyle gold.
Franklin, who won four golds at London 2012, is bidding to become the first swimmer -- male or female -- to win eight gold medals at a world championships, a feat not even 18-time Olympic gold medallist Michael Phelps achieved.
The US teenager will swim in the 50, 100 and 200m backstroke events, the 100 and 200m freestyle, with two more relays to come.
The USA won on Sunday by just 0.12 of a second from the Australians.
It was Megan Romano, swimming the anchor leg, who managed to hold off Alicia Coutts, leaving the Australian in floods of tears.
The USA nearly made it a hat-trick of titles in the men's 4x100 freestyle final, but France's Jeremy Stravius hit the wall just 0.24 seconds faster than America's James Feigen as the Olympic champions added world gold.
In a grandstand finish, four teams were still in contention, but the French hung on amidst plenty of vocal support from travelling fans.
Sweden's Sarah Sjostrom was the fastest into Monday's final of the women's 100m butterfly as the 2009 world champion clocked 57.10sec ahead of title holder, Olympic champion and world-record holder Dana Vollmer of the USA.
Vollmer was fourth fastest in the semi-finals, with Australia's Olympic bronze-medallist Coutts third.
South Africa's Olympic 100m breaststroke champion Cameron van der Burgh was joint-second fastest into Monday's final behind Australia's Christian Sprenger, the London silver medallist, who clocked 59.23 sec in the semi-finals.