Dhaka, July 29 -- 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-times 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 w...