Josh Liendo lowered his own national men's butterfly record twice and reigning Olympic champion Maggie Mac Neil won the women's butterfly at the Canadian swim trials Wednesday.

Liendo of Markham, Ont., clocked 50.78 in the 100-metre fly in the morning heats before knocking that time down to 50.36 in Toronto's Pan Am Sports Centre.

The 20-year-old claimed bronze in the event at the 2022 world championship and will race it again this summer in Fukuoka, Japan.

"I did not expect that time in prelims. I mean, prelims was more about me focusing on my technique,' Liendo said.

“Tonight was about getting fast, about me just going out fast so that’s what I did. Hurt a little on the way in, on the way back, but that’s swimming."

Runner-up Ilya Kharun of Montreal at 51.45 had the fastest time of his career. The 18-year-old will make his world championship debut in Japan.

The trials featuring 623 athletes from 148 clubs across the country are a selection event for the world championship that runs from July 14-30 in Japan, the world para swim championship from July 31 to Aug. 6 in Manchester, England, as well as the world junior championship in Netanya, Israel, and Pan American Games in Santiago, Chile, later this year.

Toronto's Summer McIntosh set a world record in the women's 400-metre freestyle Tuesday. The 16-year-old will race the 200-metre individual medley Thursday.

While Mac Neil of London, Ont., was off her own Canadian-record pace, the 23-year-old was the only woman to swim the 100-metre butterfly under 57 seconds in the final at 56.54.

Liendo and Mac Neil’s winning times were the fastest in the world so far this year.

Three-time Olympian Katerine Savard of Pont-Rouge, Que., was second behind Mac Neil in 57.81.

"Just coming in here and getting the job done, but also having fun and trying to get on that team and hopefully pull someone along too,” said Mac Neil of her first final of the meet.

“It's great for Katerine. She's done it for so long. I definitely still look up to her, she's incredible.”

Toronto's Javier Acevedo lowered his own national record in the men's 50-metre backstroke to 24.90 seconds en route to victory.

“It feels good. It's great,” said the two-time Olympian, who also won the 100-metre backstroke at trials.

“Now, just take it day by day. I got a day off tomorrow and then the 100 free. This sets me up for the rest of the week and the next couple of months.”

Reigning women's 50-metre backstroke champion Kylie Masse of Lasalle, Ont., touched the wall in 27.41 seconds just ahead of Calgary's Ingrid Wilm. The backstroke rivals qualified for the world championship on opening day when Wilm upset Masse in the 100 metres.

"I just wanted to come in and have a good race,” said Masse, who is an Olympic silver medallist in the 100. “Yesterday clearly wasn't my best and that's just all I had yesterday, and I have to take what I can from that and move forward.

“Ingrid’s an incredible swimmer, and it's been great to watch her improve over the last number of years. I’m really happy for her.”

Other winners Wednesday were 17-year-old Emma Finlin of Edmonton in the women’s 1,500 freestyle and Eric Brown of Pointe-Claire, Que., in the men’s 800 free.

Both will make their world championship debuts in the pool after racing open water last year in Budapest, Hungary.

Five-time Paralympic champion Aurélie Rivard of St-Jean-sur-Richelieu, Que., took the women's 400-metre freestyle multi-class to qualify for Manchester.

It was Rivard's first time racing the event since winning gold and setting a world record in Tokyo's Paralympics.

"I’ve only been back to full-time training since January, so I didn’t really have a specific goal in mind,” Rivard said. "I wanted to go a better time than the morning and focus on the technical aspects of my race.

“I’m just happy to see where I’m at and I think I can perform even better in August.”

Nick Bennett of Parksville, B.C., won the men’s 200 free multi-class in 1:56.38, which gave him a berth on the world para squad.

Multi-class winners who didn't reach the qualifying time for Manchester were Philippe Vachon of Blainville, Que., in the men's 400 free, Nikita Ens of Meadow Lake, Sask., in the women's 50-metre backstroke and Angela Marina of Cambridge, Ont., in the women's 200 freestyle.

Canada's top Olympic and Paralympic swimmers, as well as juniors, will compete until Sunday.