Australia's Kaylee McKeown has bounced back from a disqualification in the 200 individual medley, claiming the 100m backstroke title at the World Aquatic Championships in Japan.
The final on Tuesday night in Fukuoka pitted the reigning world champion, American Regan Smith, against McKeown, who won the 100-200 metre backstroke double at the Tokyo Olympics.
Smith led the Australian by a small margin at the halfway mark, but McKeown powered home in the second half of the race to win by a quarter of a second from her rival.
McKeown stopped the clock in a championship record time of 57.53, ahead of Smith in 57.78, with fellow American Katharine Berkoff taking the bronze in 58.25.
The win means McKeown now holds the Olympic, Commonwealth Games, world short course and long course titles for the 100m backstroke.
"Yeah, I mean it was going to be 50-50 tonight between the Americans and I so it was really good coming back on that last 50," McKeown told Channel Nine after the race.
"I think we were both hurting in that last 15 but I dug deep and gave it everything I could."
The 22-year-old was left shocked and frustrated after she was disqualified in the semi-finals of the 200 metres IM earlier in the week, after judges ruled she had committed a stroke violation between the backstroke and breaststroke legs.
"I am sure there is worse I have had to deal with but it is definitely something I have learnt from and not to take it so emotionally and just forget about it," she said.
McKeown still has the 200m backstroke event to come.
Earlier in the program, American Katie Ledecky made a one-act affair of the 1,500m freestyle final, winning by 17 seconds over Italy's Simona Quadarella, with China's Li Bingjie in third.
Australia's Lani Pallister finished fifth.
The win marked Ledecky's 20th long-course world title of her career.
In the women's 200m freestyle event, Australia's Ariarne Titmus and Mollie O'Callaghan set up a final showdown with Canada's Summer McIntosh, setting the fastest and third-fastest times for tomorrow night's final.
Titmus won her second semi-final in 1 minute 54.64 seconds, ahead of O'Callaghan in 1:54.91.
McIntosh, who missed out on the medals in the women's 400m freestyle taken out by Titmus earlier in the week, won the other semi-final in a time of 1:54.67.