Teenage swimming sensation Summer McIntosh launched her world championships with a packed programme and will go head-to-head later Sunday with Katie Ledecky as they renew their Paris Olympics rivalry.
The 18-year-old Canadian McIntosh and American great Ledecky, who is a decade older, will face off on day one in Singapore in the evening for the 400m freestyle crown.
McIntosh is the world record holder and favourite, especially with Australia's Paris Olympics gold medallist Ariarne Titmus on an extended break following the Games last summer.
McIntosh took silver in the French capital behind Titmus, with Ledecky third in the weaker of her three freestyle events.
In the morning heats on the opening day of competition in Singapore, nine-time Olympic gold medallist Ledecky fired an early warning shot and qualified fastest for the 400m final in 4min 01.04sec.
McIntosh eased through in 4:03.11, behind Ledecky and Australia's Lani Pallister.
"It's always good to get the first one out of the way and I'm looking forward to the rest of the week," said Ledecky, one of the best swimmers of all time.
With the 400m free final hours away, she added: "It'll be a great race, lots of great competitors in there. It should be a fun, fast field."
McIntosh, who broke three world records in a matter of days at the Canadian trials in the lead-up to the worlds, started her programme by qualifying second-fastest for the semifinals of the 200m medley – another event she holds the record in.
With a busy day in the pool ahead of her, McIntosh had plenty left in the tank in reaching the semis in 2:09.46, a finger tip behind Australia's Tara Kinder.
McIntosh, who won three gold medals along with her silver in the French capital a year ago to become one of the stories of the Games, is pursuing five individual titles over the next week.
Also into the semifinals in the women's 200 medley was the Chinese prodigy Yu Zidi, aged just 12.
She launched her championships by narrowly qualifying in 2:11.90, in what is not her strongest event.
The school girl will also compete at the championships in the 400m medley and the 200m butterfly.
Germany's Olympic champion and newly minted world record holder Lukas Maertens is strong favourite to win the men's 400m freestyle later Sunday.
He moved into the final second-fastest in 3:43.81 – his world record is 3:39.96 – behind chief rival Sam Short (3:42.07).
Short's Australian teammate Elijah Winnington, the Paris silver medallist, surprisingly failed to qualify for the final.