World record holder Regan Smith was fastest in the women's 100 metres backstroke preliminaries at the world championships in Singapore on Monday as the American laid down an early marker in her upcoming battle with Australia's Kaylee McKeown.
The pair have built up quite the rivalry, with McKeown completing a triumphant defence of her Olympic 100 and 200 backstroke titles when the two faced off in Paris last year, with Smith having to settle for silver in both events.
Smith came into the world championships as the top seed in the event ahead of five-time Olympic gold medallist McKeown and posted a time 58.20 on the second day of competition at the Singapore Sports Hub.
American Katharine Berkoff was second quickest with 58.55, while 2023 world champion McKeown's time of 58.57 put her in third heading into the semis later on Monday.
In the men's event, world record holder and Olympic champion Thomas Ceccon was given a scare as he only squeaked into the semifinals with the 13th-fastest time in the heats.
Frenchman Yohann Ndoye-Brouard was fastest, touching the wall in a personal best 52.30, with Russian Kliment Kolesnikov, competing as a neutral athlete, second quickest with 52.57.
Italian Ceccon's time was 1.35 adrift of Ndoye-Brouard's mark.
American great Katie Ledecky put the disappointment of missing out on the 400 freestyle title on Sunday behind her with a strong swim in her signature event – the lung-bursting 1 500 freestyle.
The 28-year-old, who is the world record holder and has won five world titles in the event, posted a time of 15:36.68, which was more than 10 seconds quicker than Australia's Lani Pallister, the winner of the second heat.
Ireland's Mona McSharry posted 1:05.99 to go through fastest in the women's 100 breaststroke heats, nearly half a second ahead of defending champion Tang Qianting of China, who was seventh quickest (1:06.45).
World record holder Lilly King was well off the pace but scraped through in 15th almost a second down on McSharry's time.
There were few surprises in the men's 200 freestyle as Olympic champion David Popovici of Romania turned up the heat in the final 50 to put down a time of 1:45.43.
American Luke Hobson qualified second fastest in 1:45.61 but China's Pan Zhanle failed to progress, the 100 freestyle Olympic champion and world record holder trailing in 22nd in the heats.
"I'm not sure what happened, and I'm not happy with this time," Pan said. "But it won't affect my upcoming races. The 200m and 100m are two different events."
In the evening programme, all eyes will once again be on Canadian powerhouse Summer McIntosh as she goes for her second gold of the meet in the women's 200 individual medley, while China's 12-year-old swimming sensation Yu Zidi is also in action.