Libby Lenton gave herself two chances to set a world record at the Australian short-course swimming championships but only needed one, smashing the 100m freestyle mark in Melbourne.

Lenton used the semi-final to set a new world best of 51.91 seconds, eclipsing the record of 52.17 held by Sweden's Therese Alshammar since 2000.

It continued a great run for the diminutive Queenslander, who won the 50m freestyle event at last week's world championships in Montreal as well as gold in the 100m medley relay.

Lenton said she went into the race with the world record in her sights, knowing that if she didn't crack it she would have another chance in the final.

"My coach Stephan (Widmer) asked me whether I wanted to hold back a bit tonight or whether I wanted to go hard and he suggested I give myself two chances of going hard so I went out tonight with that in mind, hoping to do a PB," Lenton said.

She admitted she was surprised by the time after already tapering once for the world championships, but hadn't ruled out improving on the new mark in the final Tuesday night.

"I'll have to talk to my coach but hopefully there will be things that I can improve on.

"I was surprised, I was hoping to go under 52 here ... but I was kind of a bit hesitant because I haven't been feeling the greatest after all the travelling and the extended rest period that we've had."

The 20-year-old has had a running battle in the long-course events with Australia's 100m freestyle world champion Jodie Henry, although the latter decided to skip these championships which double as trials for the world short-course championships in Shanghai next April.

Lenton relishes the shorter format, setting an Australian and Commonwealth record in the 100m freestyle event here last year before winning gold at the world championships in Indianapolis.

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