Michael Phelps put on another astonishing performance to break his own world record in the 200m individual medley.

The 23-year-old, who is expected to bid for eight gold medals in Beijing next month, claimed his fourth individual triumph of the trials by finishing the 200m IM in one minute 54.80 seconds, 0.18secs faster than last year's effort in the world championships in Melbourne, Australia.

Ryan Lochte, who posted a time of 1:55.22, finished second in the event. He also placed behind Phelps in Sunday's 400m IM, an event which saw both swimmers better the previous world record. Phelps finished first in that event with a time of 4:05.25.

Phelps then qualified fastest for the 100m butterfly final in 51.10secs, 0.42secs ahead of world record holder Ian Crocker (51.52secs).

Lochte also finished second in the 200m backstroke on Friday, with Aaron Peirsol winning by two one-hundredths of a second in a time of 1:54.32 - equal to Lochte's world record set in Melbourne in March 2007.

Rebecca Soni claimed first place with a time of 2:22.60 in the women's 200m breaststroke.

Amanda Beard, who won the event at the Athens Olympics in 2004, finished second in 2:25.13 to qualify for her fourth Olympic team.

Dara Torres, 41, won the women's 100m freestyle ahead of American record holder Natalie Coughlin.

Torres touched first in 53.78secs to qualify for her fifth Games, while Coughlin qualified in second place in a time of 53.83secs.

Ben Wildman-Tobriner qualified fastest for the men's 50m freestyle finals, clocking 21.65secs in his semi-final.

Cullen Jones, who set the American and meet records in 21.59secs in the heats, was second fastest, while Garrett Weber-Gale was third fastest and Gary Hall Jr, twice the Olympic champion, was fourth fastest for Saturday's final.

Elizabeth Beisel was the fastest qualifier for the women's 200m backstroke final in a time of 2:07.78.