The Australian, aiming to become the first swimmer to win the same event at three successive world championships, clocked three minutes 47.44 seconds in a comfortable swim to win the final heat from promising young Russian Yuri Prilukov (3:48.49).

Thorpe became the youngest men's world champion ever when he won the 400m freestyle in Perth in 1998 at the age of 15. He retained the title in Fukuoka, Japan [ Images ], in 2001 when he won six gold medals, a record at a single world championships.

Team mate Grant Hackett, silver medallist behind Thorpe in Perth and Fukuoka, won the preceding heat in the second-fastest overall time of 3:48.35 from Massimiliano Rosolino of Italy [ Images ].

Rosolino, who was silver medallist behind Thorpe at the 2000 Sydney Olympics [ Images ], clocked 3:49.59, finishing just ahead of Britain's Graeme Smith [ Images ] (3:49.92).

Both qualified for the evening's final. But fellow Italian Emiliano Brembilla, bronze medallist in 2001, failed to make it, touching a distant sixth in his heat in 3:53.43.

American Jenny Thompson, the 1998 world champion, set a championship record 58.14 seconds to lead the semi-final qualifiers in the women's 100m butterfly.