Pellegrini had previously also held the world record of 4:00.41.

Biedermann, meanwhile, was an unlikely winner in the men's 400m freestyle as he took the gold medal in a race he did not at first want to swim.

The 22-year-old, who said before the heats in the morning that he would scratch from the final if he scraped through with the seventh or eighth-fastest time, set a new European record in the heats and then decided to swim the race.

After only lying fourth at the 100m mark, Biedermann started pushing forward and managed to edge out Tunisian Oussama Mellouli, who won silver two years ago at the worlds in Melbourne.

Biedermann finished in a time of 3:40.07, beating Ian Thorpe's world record from 2002 by one hundredth of a second.

Mellouli won silver, 1.04 seconds off the pace, while the bronze medal went to Chinese swimmer Zhang Lin in a time of 3:41.35.

Biedermann, who had invited his family and girlfriend to Rome to watch him swim, dedicated his victory to his grandmother, who celebrated her 73rd birthday.

In the first event of the evening, Swedish teenager Sarah Sjostrom broke the world record in the women's 100m butterfly.

The 15-year-old sensation, who had already broken the championship record in the morning heats, managed a 56.44 seconds time in the semi-finals, beating Inge De Brujn's time of 56.61 by. 17 seconds.

In the semi-finals of the women's 200m individual medley American Ariana Kukors took more than one second off Stephanie Rice's world record when she qualified for the finals with a 2:07.03, beating the old record of 2:08.45 by 1.42s.

Rice also comfortably qualified for the finals with the second-fastest time.

The defending champion in the men's 50m butterfly, South African Roeland Schoeman, who set a championship record in the morning heat's with a 22.90, sensationally failed to qualify for the finals as he posted the ninth-fastest time.

He finished in a time of 23.18.

Spain's Rafael Munoz, who equalled Schoeman's time in the heats, had the fastest time in the semi-finals when he won his heat in the new championship record-time of 22.68.

American Eric Shanteau broke the championship record in the men's 100m breaststroke semi-finals with a time of 58.96 to qualify as the fastest for the finals.