Swimming-'Terminator' Titmus gunning for Ledecky at worlds

MELBOURNE, July 16 (Reuters) - Ariarne Titmus earned the nickname "Terminator" after blitzing her rivals as a schoolgirl sensation and now the Australian teenager has her sights locked on American powerhouse Katie Ledecky at the world championships in Gwangju.

The 18-year-old from the island state of Tasmania clocked the year's best time of 1:54.30 in the 200 metres freestyle at national trials in April and is only 0.07 seconds adrift of Ledecky's year-best mark of 3:59.28 in the 400.

Five-times Olympic champion Ledecky has set the benchmark in middle and long distance swimming since she stunned the world as a 15-year-old to claim the 800 gold at the 2012 London Games.

But Titmus has provided something the American has not been used to -- competition.

In a battle royale at last year's Pan Pacific Championships, Titmus pushed the 14-times world champion to the limits in the 400, finishing a body length behind Ledecky and clocking a time of 3:59.66 to become only the third female swimmer to break four minutes in the distance.

Ledecky's 3:58.50 was some way off her world record of 3:56.46 at the 2016 Rio Games but the American had never been so tested before.

Although Titmus claimed three titles at her home Commonwealth Games on the Gold Coast last year and the 200 and 400 short course world titles in Hangzhou in December -- all without Ledecky competing -- the Australian felt the Pan Pacs 400 showdown was the high point of her year.

"The Commonwealth Games was probably at the time the biggest thing but for me the elation of breaking four minutes in the 400 probably had the biggest effect for me," she said in an interview with local broadcaster Seven Network.

"I still think about the fact that only two other women in the world have done that."

Ledecky is unlikely to take the challenge lying down as she bids to extend her record world title haul in South Korea, and Titmus welcomed the prospect of having to raise her level again.

"If you don't have something to chase, you probably don't want it as bad. Without (Ledecky) I definitely wouldn't be swimming as fast as I am," she said.

"I know exactly what I have to do.

"I hope she keeps getting better so that I can get better."

Titmus anchored Australia to bronze in the 4x200 relay at the last world championships in Budapest in 2017 and finished fourth in the 400 in her maiden international meet.

She has more recently become a force in the 800 and has the year's fifth best swim over the distance after leader Ledecky, China's Wang Jianjiahe and American Leah Smith's times.

Titmus may be some way from threatening Ledecky's reign over the distance but is encouraged that her natural speed has improved over the past year to allow her to compete meaningfully

"Deep down the 800's my least favourite probably because it's the longest," she said.

"I struggle to focus for that long. (Coach) Dean (Boxall) calls me a frisbee in the wind." (Editing by Peter Rutherford)