Australia's "Deadly Medley" team of Matt Welsh, Jim Piper, Geoff Huegill and Ashley Callus tonight smashed the world record in the men's 4 x 100m medley relay in an exciting climax to night three of the Telstra Australian Short Course Championships at the Melbourne Sports and Aquatic Centre.

In a special time trial, the Aussie foursome set out to break the world mark of 3 minutes 29.00 seconds, set by the USA at the world short course championships in Moscow in April - and they delivered in style - stopping the clock in 3:28.12.

Welsh, who broke the 50m world record on night one, gave the team a tremendous start, setting a new Commonwealth 100m record of 50.95 in the opening leg, and smashing the split of American Aaron Piersol (52.17) from the USA's world record setting team.

Welsh handed over to Commonwealth Games gold medallist Jim Piper, who lifted to clock a time of 59.44 to keep the team under world record pace at the half-way mark.

Geoff "Skippy" Huegill dived in with the crowd cheering as one, and split a 50.61, under the 51.93 of American Peter Marshall before handing over to Ashley Callus still under world time.

Callus stormed home in a sizzling 47.12 to touch for a final time of 3.28.12 to demolish the USA's world record by 0.88 of a second to a rapturous ovation from the crowd.

The tired foursome were thrilled with the effort, Piper admitting afterwards that taking back the world record had been on their minds for months.

"We've been talking about this amongst ourselves since the morning after we came second to the Americans at the World Short Course Championships," Piper said.

"We're all pretty tired after the last couple of months, and to finish with that, it's just incredible."

Welsh said: "I'm really glad I did it to lead off these guys, and did it when it counted."

The stunning swim capped off an exciting night three of racing.

Earlier, Dyana Calub took her second gold of the meet in the women's 50m backstroke, winning in 28.29 ahead of fastest qualifier through the semi-finals Nicole Seah, who won silver in 28.47.

Asked about the youngsters challenging her, Calub said she hoped to continue her winning ways.

"It's a bit scary," Calub said, "but I'm just going to keep working and hopefully keep coming through."

Bronze went to Melbourne Vicentre's Rachel Goh in 28.70.

In the women's 100m IM Commonwealth Games silver medallist Brooke Hanson swam a tremendous back half of the race to win gold in 1.01.46, the second fastest time ever by an Australian.

Winner of the 50m and 200m breaststroke already at this meet, Hanson established a half body length lead in the breaststroke leg and held on over sprint freestyle specialist and Pan Pac gold medallist Alice Mills, who took the silver in 1.01.66.

"I'm really happy with that time," Hanson said after the race. "It's my best time, and to win gold is just awesome."

The bronze medal went to promising Carey Aquatic swimmer Shayne Reese in 1.02.01.

Michael Klim, winner of the 200m freestyle on night one, continued his fine comeback to racing after undergoing back surgery in February by qualifying fastest for the men's 100m freestyle final in 48.58.

Alongside Klim in tomorrow night's final will be Nunawading duo Andrew Dyson (49.38) and Jared Clarke (49.65), and the pair of Casey Flouch (Commercial) and Antony Matkovich (City of Perth) who dead-heated the first semi-final in 49.38.

Well-travelled Michelle Engelsman, a former national long course champion, streaked home in the women's 50m freestyle to win the sprint crown in a time of 22.20 ahead of River City's Marieke Guehrer, who took silver in 22.22.

Engelsman just missed the Commonwealth and Pan Pac teams, and had to watch the action from home. "I haven't had the best year in the last twelve months, and to come back here and win is really great," she said.

The bronze went to the fastest qualifier through the semi-finals, Southern Crawl's Nichola Chellingworth in 22.28.

Joshua Krogh of the AIS lead from start to finish in the men's 200m butterfly to win by a body length from the rest of the field, touching in 1.56.77 to take gold and his first national title.

"It hurt a bit watching the Commonwealth Games and Pan Pacs knowing I had the chance to be there," he said after the race, reflecting on just missing the Telstra Dolphins squad this year.

"But hopefully I can keep working and be there next time."

Silver went to a fast-finishing Shane Fielding of Waterworx in 1.58.61, and the bronze to Campbelltown's Matthew Hall in 1.58.68.

Versatile world champion Petria Thomas, who said breaststroke was the only discipline she would not contest, continued her winning form at these championships, taking out the women's 400m freestyle in 4.07.26.

An event she has not entered in five years, Thomas took the race out hard and led by a body-length from fellow Telstra Dolphin and winner of the 800-1500m double at this meet Amanda Pascoe, who touched in 4.08.74 for the silver.

Bronze went to Toongabbie's Belinda Wilson in 4.12.31.

Matt Welsh, who set a world record on night one in the 50m backstroke and just missed the 200m world mark last night, qualified fastest for the final of the men's 100m backstroke final tomorrow night, with his sights now set on his new Commonwealth record of 50.95.

Welsh cruised through his semi-final in 53.54, while Victoria Park's Matthew Spicer won the first semi-final in 53.93.

Other contenders in the final include CJ Aquajets Ashley Anderson (53.90) and Telstra Dolphin Ethan Rolff (54.04).

In the women's 100m breaststroke semi-finals Olympian Tarnee White won her race to qualify fastest for the final in 1.07.48, one one-hundredth of a second ahead of club team-mate and fellow Telstra Dolphin Liesel Jones, who won her semi-final in 1.07.49.

The Redcliffe Leagues Lawnton duo will face tough competition from defending champion Brooke Hanson, winner of the 50m and 200m at this meet, and Sarah Kasoulis (Carey Aquatic), Jade Edmiston (Southern Crawl), and Katie Regan (Redlands).

Veteran Phil Rogers stormed home to win the men's 100m breaststroke in 1.00.22, his 12th win in the event in his career, just pipping long course national champion and Commonwealth Games gold medallist Jim Piper, who took the silver in 1.00.26.

Rogers expressed some surprise at the win. "I'm not really fit enough," he admitted. "That's really surprised me, but I'm really happy."

Bronze went to Knox Pymble's James Beasley in 1.00. 61.

The women's 100m butterfly semi-finals saw world champion Petria Thomas qualify fastest for tomorrow night's final, breaking the minute mark to win her semi-final in 59.73.

Thomas will be going for her third gold of the meet after taking out the 50m and 200m butterfly earlier in the week. She will face tough competition in the final from fellow Telstra Dolphins Felicity Galvez (59.91) and Rachel Coffee (1.00.34), and Campbelltown's Lara Davenport (1.00.19).

In the women's 4 x 100m Freestyle relay the Chandler A team of Jodie Henry, Cassie Hunt, Melanie Houghton, and Alice Mills won gold in a new club record of 3.39.71 ahead of Carey Aquatic, who took silver in 3.43.85.

Bronze went to the Chandler B team in 4.48.70.