Ryan Lochte broke two world records in under two hours and helped his more famous American teammate Michael Phelps collect his fifth gold medal at the World Swimming Championships on Friday.

Lochte broke Aaron Peirsol's record in the 200 backstroke final before teaming up with Phelps as the United States demolished Australia's mark for the 4x200 freestyle relay.

Phelps, who swam the lead-off leg in the relay, edged closer to breaking Ian Thorpe's record of six gold medals at a world championships when he collected his fifth in as many events.

The 21-year-old also booked his place in Saturday's 100 butterfly final and has another two events on Sunday to complete his bid to scoop an unprecedented eight titles.

Libby Lenton bagged her third gold medal in Melbourne by beating the fastest field ever assembled to win the women's 100 freestyle and her Australian teammate Leisel Jones completed the 100-200 breaststroke double for the second time.

Japanese Olympic champion Kosuke Kitajima capitalized on the absence of American rival Brendan Hansen to win the men's 200 breaststroke final and provide Asia with its second gold medallist this week after South Korean Park Tae-hwan in the 400 freestyle.

Lochte sliced 0.12 off Peirsol's mark when he beat his teammate in a sprint finish to reach the wall first in 1:54.32.

Peirsol, swimming in the lane next to Lochte, had to settle for the silver medal with Austria's Markus Rogan taking the bronze.

It was Peirsol's first defeat in the event since he finished second to Lenny Krayzelburg in the Olympic final at Sydney in 2000, ruining his bid to join Australian long-distance freestyler Grant Hackett as the only swimmers to win the same event at four world championships.

"Ryan swam a wonderful race, can't take that away from him. He definitely earned it," Peirsol said.

Lochte had finished second to Peirsol in the 100 backstroke final and was runner-up to Phelps in the 200 individual medley but struck gold twice when he followed up his breakthrough win in the backstroke with another victory in the relay.

Lochte and Phelps joined forces with Klete Keller and Peter Vanderkaay to win the gold in a time of 7:03.24, slashing 1.42 off the previous record of 7:04.66 set by a Thorpe-led Australian team at the 2001 world championships in Fukuoka, Japan.

It was the 12th world record in the past four days at the championships.

(China Daily via agencies March 31, 2007)