Fans have flocked to the diving, open water and synchronised swimming during the first seven days of competition in Barcelona and the hilltop Palau Sant Jordi is now gearing up for what should be a scintillating week of racing in the specially constructed 50 metres pool.
Sun's qualifying time of three minutes 40.17 seconds is only a tenth of a second outside the world best set by Paul Biedermann of Germany at the 2009 world championships in Rome when swimmers were still wearing the body suits that helped smash a slew of records.
The main challengers for the Olympic champion, who is also strongly fancied for the 800 and 1,500 freestyle, are likely to be David Mckeon of Australia, U.S. pair Connor Jaeger and Matt McClean and Japan's Kosuke Hagino.
Muffat, who also won silver in the 200 metres freestyle in London behind American Allison Schmitt, is the fastest woman in the 400 this year and a hot favourite to get the better of the likes of Schmitt's compatriot Katie Ledecky, Australian Bronte Baratt and Britain's Jazmin Carlin.
The day concludes with the 4x100 metres relays, where traditional powerhouses United States and Australia will be the favourites in the men's event with the French and Russians.
The Americans and Australians will also be the teams to beat in the women's event, with the Netherlands, silver medallists in London, strong contenders.
- Sports & Recreation