|Sun Yang of China reacts after competing in the men's 800m freestyle heats during the World Swimming Championships at the Sant Jordi arena in Barcelona July 30, 2013. REUTERS/Albert Ge|
Sun matched a feat previously achieved only by Grant Hackett when he claimed the 400 freestyle title on Sunday to become the second man only after the Australian to claim world titles at 400, 800 and 1,500 metres.
His three titles came at two different championships - he won the 800 and 1,500 in Shanghai two years ago and was second in the 400 - but he is now on course to match Hackett's three golds from the 2005 edition in Montreal.
American teenager Missy Franklin can win her third gold in three finals contested this week when she lines up in the 200 metres freestyle.
Olympic silver medallist Camille Muffat of France is likely to pose a strong threat to the 18-year-old, while world record holder and defending champion Federica Pellegrini cannot be discounted after going fastest in Tuesday's semi-finals.
The 24-year-old's qualifying performance was a surprise as she said before the championships she was focusing on the 200 metres backstroke.
Two other finals are scheduled for Wednesday.
South Africa's Chad le Clos caused a sensation when he beat Michael Phelps to win 200 metres butterfly gold at the London Olympics and he was quickest in Tuesday's semis.
In the men's 50 metres breaststroke, Le Clos's compatriot Cameron Van Der Burgh swam 0.11 seconds outside his own world record to top qualifying.
Australian Christian Sprenger, who beat Van Der Burgh into second place to win the 100 metres breaststroke gold on Monday and is chasing his nation's first gold at the shorter distance, was fourth quickest in 27.30.
(Reporting by Iain Rogers; Editing by John Mehaffey)