Summer McIntosh set her second world record of the week Saturday, winning the 400m individual medley at the Canadian Swimming Trials in 4min 25.87sec.
The 16-year-old sensation broke the record of 4:26.36 set by Hungarian Katinka Hosszu at the 2016 Rio Olympics.
McIntosh had opened the meeting, Canada's selection meet for the World Championships in Fukuoka, Japan, in July – with a world record in the 400m freestyle.
Her time of 3:56.08 in the 400m free broke the record of 3:56.40 set last May by Australia's Ariarne Titmus at the Australian Championships in Adelaide – where Titmus broke American Katie Ledecky's six-year-old mark.
McIntosh is the youngest swimmer to break a long course swimming world record in an individual Olympic event since Ledecky in 2013.
"Obviously it's really amazing and I'm really happy to get another world record," McIntosh said in an pool-deck interview.
"Right now I'm just thinking about my legs," she added, letting her knees sag for a moment before adding: "They hurt so bad.
"The 4IM is one of the toughest events out there so going into tonight I just tried to mentally prepare for that," she said. "Whatever the time was the time would be."
McIntosh, who won 200m butterfly and 400m medley gold at the World Championships in Budapest last year, fell behind world record pace after the penultimate breaststroke leg of the medley final, but rallied on the closing freestyle.
"In the freestyle I always like to look at the clock and I think I saw 26.1 or something and I thought, just go, go crazy," she said.
"I just gave it everything I've got and I knew it would be close."