Phelps breaks own record

Phelps shaved nine hundredths of a second off his previous record of 1:53.80, which he set at the Pan Pacific Championships on August 17.

It was the fifth time the 21-year-old has broken the 200 metres butterfly world record, one of the six events he captured a gold medal in at the 2004 Athens Olympics.

Phelps said he hoped to go even faster when he swam the event in next month's world championships in Melbourne, Australia.

"I didn't think I was going to break a record tonight," he told reporters.

"I could tell something good was happening when I heard the crowd yelling," added Phelps, who led by four body-lengths at the 150-metres mark, which brought the packed crowd at the Mizzou Aquatic Center to its feet.

"But when I looked up at the clock I thought it said 1:56," he added.

However, a second inspection made him realise how fast he had completed the race.

"When I took off my goggles and saw the time, you could tell that my reaction changed a little bit, and I basically went nuts," Phelps said.

"I definitely did not expect that tonight."

Phelps, who won a total of eight medals at the Athens Games and is swimming six events in the Missouri meeting, said his performance came as a result of some solid training.

"A lot of our practice has been focused on underwater kicking, and I know that the more kicking I do, the faster I can go," he said.

"Coming off the wall well when people are getting tired is a good weapon to have. We have wanted to work on it and it's starting to show now."