MONTREAL, July 30 - Ian Crocker demolished the world record to win the 100 metres butterfly at the world swimming championships on Saturday and ruin Michael Phelps's dream of winning six gold medals.

Crocker stormed through two laps of the Montreal pool in 50.40 seconds to wipe 0.36 off the previous mark which he set at last year's U.S. Olympic trials at Long Beach, California, and retain the world title he won at Barcelona in 2003.

Phelps was unable to match Crocker's incredible speed and had to settle for second place in 51.65 while Ukraine's Andriy Serdinov was third in 52.08 on the penultimate day of the championships.

Crocker's win avenged his gut-wrenching loss to Phelps in last year's Olympic final when he led all the way but misjudged his touch on the wall allowing Phelps to sneak through.

It also destroyed Phelps's bid to match Ian Thorpe's record of six gold medals at a single world championship. Phelps has won four golds and a silver in Montreal.

"When racing against Michael I know I need a world record to beat him," Crocker said. My goal was to break the world record but I didn't think it would be by that much."

Leisel Jones collected her third gold medal as part of the Australian team that won the women's 4x100m medley relay while her 17-year-old compatriot Danni Miatke won her first world title with an upset win over Swedish world record holder Anna-Karin Kammerling in the 50m butterfly final.

South African sprinter Roland Schoeman, Zimbabwean backstroker Kirsty Coventry and American long-distance swimmer Kate Ziegler all won their second gold medals of the championship.

Schoeman powered his way down the pool in 21.69 to win the 50m freestyle splash and dash with the second fastest time in history, just 0.05 outside Alexander Popov's world record.

Duje Draganja of Croatia finished second in 21.89 while Bartosz Kizierowski of Poland was third in 21.94 but neither could keep up with Schoeman, who set a world record to win the 50m butterfly earlier this week and was second in the 100m freestyle final.

Coventry broke her own African record to add the 200m backstroke title to her earlier win in the 100m, leading all the way to reach the finish wall in 2:08.52. American Margaret Hoelzer finished second in 2:09.94 while Japan's Reiko Nakamura was third in 2:10.41.

Ziegler, 17, also produced a bold front-running display to win the 800m freestyle in 8:25.31 following her runaway victory in the 1500m won earlier this week.

Canada's Brittany Reimer finished second in 8:27.59 while Japan's Olympic champion Ai Shibata was third in 8:27.86.

Jones, who the 100m-200m breaststroke double earlier in the week, teamed up with Sophie Edington, Jessicah Schipper and Libby Lenton to win the medley relay for Australia in a combined time of 3:57.47, just 0.15 outside the world record Australia set at last year's Athens Olympics.

The U.S. finished second in 3:59.92 after leading for the first 150m while Germany were third in 4:02.51.