Peirsol led from start to finish in the 200m backstroke

His time of one minute 54.74 seconds - more than half a second ahead of his previous mark - saw him win his eagerly awaited clash with Michael Phelps.

But Phelps qualified in second place to stay on course in his attempt to surpass Mark Spitz's haul of seven Olympic golds.

Meanwhile Amanda Beard regained her world record in the 200m breaststroke.

Beard clocked 2:22.44 to break the record of 2:22.96 set just two days ago by Australian Leisel Jones in Brisbane.

Spitz backs Phelps

Phelps had to compete in three races on the sixth day of the trials in California and was relieved to take two further steps towards his Olympic goal.

"I am happy it's over. It's good to get that out of the way. I know I can do that schedule in Athens," said the 19-year-old.

He has now qualified to compete in five individual events in this summer's Games and a first or second place in the 100m butterfly on Tuesday will bring that number to six.

With three relay spots also possible, Phelps has the potential of winning nine gold medals in Athens.