Grant Hackett sets out Friday to create Olympic history as the first male swimmer to win three consecutive titles in the gruelling 1500 metres freestyle at the Beijing Olympics.

　　The 28-year-old Australian, who has six career Olympic medals, three of them gold, has been under pressure in the leadup to his Beijing campaign after a poor world championships by his standards in Melbourne in March 2007.

　　Poland's Mateusz Sawrymowicz ended Hackett's four-title domination of the 1500m with victory last year and the Australian also lost his 400 free world crown.

　　The general consensus is that contenders will have to swim under 15 minutes just to get into Sunday's final in what is being billed as the hottest field ever to contest the 30-lap marathon.

　　Age and times are catching up with Hackett, and he struggled to keep pace with his younger rivals as South Korean teenager Park Tae-Hwan sprinted away with last Sunday's 400m freestyle final with the Australian trailing in two seconds behind in sixth.

　　"I think I'm swimming faster than I was in Sydney and Athens and I've just got to get up and do it," Hackett said.

　　"To win I'm going to need to swim faster because the standard and the depth of the other swimmers has picked up a lot.

　　"I can't control how fast others can swim, but I can control how I go and I've done that to the best of my abilities. Physically, I feel like I've done everything."

　　His rivals are queueing up to deprive Hackett of his quest for Olympic history with his world record 14:34.56 still standing from 2001.

　　"The depth is amazing so who knows what can happen when all those people come together and have a one-off race," Welsh rival David Davies said ahead of Friday's opening heats.

　　"The world record is phenomenal. (Australian) Kieren Perkins swimming 14:41 (previous record) was something special and for Grant to beat that by seven seconds is still unbelievable now."

　　US swimmer Dara Torres is the sentimental favourite to win the women's 50m freestyle.

　　She is finding a whole new set of fans as she tackles her fifth Olympics at the unlikely age of 41.

　　"I just want to go out there for those 40-something girls and show that age is just a number," said Torres, who won the first of her nine Olympic medals in Los Angeles way back in 1984.

　　Since then she has retired twice, coming back the first time to compete in the 2000 Sydney Games, and given birth to daughter Tessa, now two years old.

　　Torres will be vying with world record holder Libby Trickett of Australia and leading Europeans Britta Steffen, Therese Alshammar and Marleen Veldhuis for gold.

　　The American men will be bidding to give Michael Phelps the favoured middle lane in the 4x100 medley final as he chases a record eight Olympic gold medals.

　　The strong Australian women's team is favoured to defend its 4x100 medley Olympic title with the heats getting underway on Friday.