Britain's David Davies set a new British record as he qualified fastest for the men's 1500m freestyle final.
Davies touched in 14 minutes 57.03 seconds, more than four seconds faster than Olympic champion Grant Hackett, who has not been beaten in the event for seven years.
Hackett was third fastest, posting a time of 15:01.89, just behind Russian Yuri Prilukov (15:01.02).
Britain's Graeme Smith also qualified as seventh quickest with 15:07.45.
Davies, 19, took 0.9 seconds off the British record he set in the Olympic trials in April.
"It felt really good," said Davies. "I was the last guy to swim in the team so I have been itching all week.
"Going under 15 minutes in the heats has only been done once before, but hopefully I can go faster in Saturday's final. I have got nothing to lose."
Australian Keiren Perkins swam under 15 minutes in the Olympic heats in Sydney four years ago.
He ended up taking silver behind Hackett, who is undefeated in the 1,500m since 1997 - a run that includes three world titles, two Commonwealth Games titles, three Pan Pacific titles, the Sydney gold and the world record.
Smith, who had been Britain's last medallist until Stephen Parry's bronze in the 200m butterfly earlier this week, added: "It's the best time I've done this year and a morning swim as well.
"There were five or six great guys in our heat and my main aim was to make
sure I was in the top two or three.
"Looking to the final, Dave is obviously in great shape, Grant is obviously
up for a medal as well, but I think anyone who makes it into the final has got a
chance of a medal of some colour."