(Reuters) -Katie Ledecky showed it will take a monumental effort to pry the 800 metres freestyle title from her grip after the American great came home more than five seconds quicker that Summer McIntosh in the world championships heats on Friday.
Ledecky, a four-time Olympic and six-times world champion in the event, posted a time of eight minutes and 14.62 seconds, with Australian Lani Pallister second quickest (8:17.06) and 18-year-old Canadian McIntosh third fastest (8:19.88).
McIntosh is attempting to match Michael Phelps's record of five individual titles at a single world championship and while she already has three in the bag, beating Ledecky in the 800 looks like her biggest challenge.
Ledecky, 28, broke her own 800 world record in May, swimming 8:04.12 to improve a mark she set nearly a decade ago at the Rio Games, but McIntosh has been making waves in the event.
She posted the third-fastest time ever in June and ended Ledecky's 13-year unbeaten streak in 2024 when she bested the American at a sectionals meeting in Florida.
McIntosh said she had been conserving energy for the final.
"My goal was just to win my heat, to pretty much secure that I'll get a lane for tomorrow night's final, and do that with the least amount of energy possible," she added.
Serbian Andrej Barna was quickest in the men's 50 freestyle heats (21.44), with Olympic champion Cameron McEvoy of Australia fourth (21.53).
McEvoy's compatriot Kyle Chalmers, a former Olympic and world champion in the 100, failed to make the semi-finals while David Popovici pulled out of the event after sealing both the 100 and 200 titles this week.
Kaylee McKeown topped the women's 200 backstroke heats with a swim of 2:08.01, while her American rival Regan Smith was fifth fastest with 2:08.65.
Defending champion Claire Curzan, who completed a world 50, 100 and 200 backstroke treble in Doha last year, was third quickest.
Swiss Noe Ponti was top seed into the men's 100 butterfly semi-finals with a time of 50.68, leading a tight field of 16 swimmers who were all separated by just 0.9 seconds.
There were some concerns over Gretchen Walsh's fitness when she withdrew from the 100 freestyle prelims on Thursday, after sickness swept through the U.S. team camp in the lead-up to the meet, but she squashed those fears by topping the 50 butterfly heats with a time of 25.22.
Olympic champions Britain will be favourites for the men's 4x200 freestyle relay gold in the evening session after finishing quickest (7:03.98) in the heats.
The evening programme will begin with Australian Mollie O'Callaghan's attempt to add the 100 freestyle title to her 200 crown.
Medals will also be handed out in the men's 200 breaststroke and 200 backstroke, as well as the women's 200 breaststroke.
(Reporting by Aadi Nair in Bengaluru; Editing by Peter Rutherford)
