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.
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.
"That race was always going to be a showdown, an exciting dogfight," King told reporters.
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"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.
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.
