Jenny Thompson smashed the championship record twice in winning her third gold medal as the Star Spangled Banner signalled a dominant night in the pool for the United States at the world swimming championships in Perth yesterday.

Thompson, the outstanding female swimmer of the championships, added the 100-metres butterfly to her earlier 100m freestyle and 100m freestyle relay gold medals as the US shot away at the top of the table with eight golds from 18 events and still three days' of competition remaining.

Thompson's ebullient form as the Chinese women retreated under the shame of four positive drug test results, spearheaded a powerful American showing on the fourth night in the pool. The five-times Olympic relay gold medallist followed up her earlier successes to beat Japan's Ayari Aoyama.

Thompson, who broke the championship record in the morning heats in 58.91 seconds, shattered the mark again in clocking 58.46. Aoyama, who maintained an underwater surge from the starting blocks for about 40m, won the silver medal with Australian Petria Thomas third in a new Commonwealth record of 58.97.

"This one means the most to me so far because it's my fastest by five-tenths of a second and I love this event," said the 24-yearold aspiring doctor. Ukrainian-born Lenny Krayzelburg kicked it off for the US with victory in the 100 metres backstroke and the men maintained an unbeaten stretch in both the world championships and Olympics by yet again landing the 100m freestyle relay.

Krayzelburg prevailed in a blanket finish to claim the backstroke crown. The 22-year-old beat Canadian Mark Versfeld by 0.17 seconds in 55.00 to take the gold medal.

"There were lots of nerves but this was a race not about time," said Krayzelburg."It's about winning and the entire race was a good one - you've got great guys in there who have come second and third at the Olympics."

There was also a stirring victory for Australian youngster Ian Thorpe, who touched out teammate Grant Hackett to claim the 400m freestyle gold. Thorpe (15) came with last-lap surge to overhaul the front-running Hackett and win by 0.15 seconds. His times of three minutes 46.29 seconds was the fourth fastest in history, with Hackett touching the wall in 3:46.44 ahead of Britain's Paul Palmer (3:48.02).

Hungary's European champion Agnes Kovacs swooped to win the women's 200m breaststroke, setting a championship record.