The world championships came alive as Lilly King of the United States won the women's 100 metres breaststroke title in one of three world-record swims at the end of a breathtaking evening session.
Adam Peaty of Britain continued his breaststroke trailblazing with his second world mark of the day to reach the 50m final and Canada's Kylie Masse produced a world-best time to win the women's 100m backstroke gold medal.
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If the day belonged to Peaty, the evening will be long remembered by Olympic champion King, who posted one minute 4.13 seconds to overhaul the world-record mark set by Lithuania's Ruta Meilutyte in 2013.
King held off the threat of Russian rival Yuliya Efimova, in a race billed as a grudge rematch of their acrimonious Olympic final, and the US secured a memorable one-two as Katie Meili touched for silver in one minute 5.03 seconds.
![World-record holder: Kylie Masse of Canada poses with the gold meda.](http://web.archive.org./web/20170803141747im_/https://www.fairfaxstatic.com.au/content/dam/images/g/x/i/r/a/0/image.related.articleLeadwide.620x349.gxir6z.png/1501018237719.jpg)
"That race was always going to be a showdown, an exciting dogfight," King told reporters.
"We get a lot of rivalries like this in football, basketball, swimming where we see a lot of really nice people, being really nice.
"That's great and all but it's not my personality. I'm spunky, I'm confident and I'm not going to not be myself before a race."
King, 20, has voiced her disapproval at Efimova being allowed to compete at global level after the Russian had twice been caught using banned substances.
![Emily Seebohm (R) won Australia's only medal of the session.](http://web.archive.org./web/20170803141747im_/https://www.fairfaxstatic.com.au/content/dam/images/g/x/i/r/a/1/image.related.articleLeadwide.620x349.gxir6z.png/1501018237719.jpg)
The spiky relationship continued in Budapest with King celebrating her world record wildly and failing to make eye contact with Efimova who had to settle for bronze.
A stunned Peaty became the first man to dip below 26 seconds in the 50m breaststroke.
By touching in 25.95 seconds, he lowered his record mark from the morning's heats by a massive 0.15 seconds.
"I was on such a massive high from this morning and it was so hard to ignore the fact that I did a world record in the morning and try to get myself emotionally ready," Peaty told reporters.
Masse produced an outstanding world-record swim of 58.10 seconds as Australia's quiet world championships continued with Emily Seebohm failing to defend her title.
AP
HOW THE AUSTRALIANS FARED ON DAY THREE
* Women's 100m backstroke final
Emily Seebohm (58.59 seconds) - bronze.
* Men's 100m backstroke final
Mitch Larkin (53.24) - sixth.
* Women's 200m freestyle semi-finals
Emma McKeon (one minute, 54.99 seconds) - second-fastest qualifier for Wednesday's final.
* Men's 200m butterfly semi-finals
Grant Irvine (1:56.33) - 12th, missed final.
David Morgan (1:57.66) - 16th, missed final.