KAZAN, Russia (AFP) - Katie Ledecky of the US wrote swimming history again at the world championships on Tuesday as three records fell, while Australia won backstroke double gold.
Ledecky underlined her status as the star of the Kazan pool by demolishing her own 1500m freestyle record in Tuesday's final, then qualified for Wednesday's 200m freestyle final less than 30 minutes later.
She may have only just graduated from High School in Maryland, but Ledecky broke a world record for the ninth time in two years when she shaved 2.23 seconds off her 1500m personal best to clock 15 minutes, 25.48secs.
"Today was a really tough day for me, I knew I was going to have this double and I was prepared for it," she said having already broken the 1500m record in Monday morning's heats.
"It hurt a lot, but I got the job done and it feels really, really good right now."
Ledecky's exploits came after South Africa's Cameron van der Burgh had broken the men's 50m breaststroke record in the morning's heats, only to see Britain's Adam Peaty swim a new record of 26.42secs in the evening's semi.
It promises to be another breaststroke battle royal between the pair in Wednesday's 50m final as Van der Burgh swam 26.74secs in his semi.
"It's going to be a good final between me and Cam as always. We'll put on a good show, I think," promised Peaty, who beat the South African on the wall in Monday's 100m final.
GUY'S SHOCK WIN
The biggest surprise of the night was James Guy's stunning win in the 200m freestyle final as the Briton beat China's Sun Yang at the wall as the 19-year-old left some big names in his wake.
He was just 0.06secs ahead of China's long-distance expert Sun who had to settle for silver while Germany's world record-holder Paul Biedermann took bronze at 0.24secs.
Ryan Lochte of the USA, who had led early on, was fourth at 0.69secs back.
"I never thought I'd race Ryan Lochte head-to-head like that, he is one of my heroes," grinned Guy, who is making his world championship debut in Kazan.
"Being world champion hasn't sunk in quite yet, I am so happy."
The teenager adds gold to the silver he won on Sunday in the men's 400m freestyle final when Sun retained his world title from Barcelona two years ago.
Sun can claim his second gold in Kazan when he looks to retain his 800m freestyle title in Wednesday's final.
Australia struck double gold as Mitchell Larkin and Emily Seebohm won the men's and women's 100m backstroke finals within minutes of each other.
Larkin, 22, claimed his first world title while Seebohm bounced back from dislocating her knee in a riding accident in May to win her first individual world title.
Larkin touched the wall at 52.40secs with France's Camille Lacourt taking silver at 0.08secs back and Olympic champion Matt Grevers earned bronze at 0.26secs.
Seebohm, who also won a relay gold on Sunday, timed 58.26secs with team-mate Madison Wilson taking silver at 0.49secs and the 23-year-old was in tears during the medal ceremony when the Australian anthem was played.
Yuliya Efimova then won hosts Russia's first swimming gold, just five months after completing a 16-month ban for taking steroids.
Efimova clocked one minute, 05.66 secs leaving Olympic champion Ruta Meilutyte of Lithuania, who had led at the halfway stage, to settle for silver at 0.70secs back with Jamaica's Alia Atkinson earning bronze at 0.76.
Meilutyte, 18, did not attend the post-final press conference, as she went to be drugs tested, and none of the six questions posed to Efimova in Russian were about her ban.
Hungary's Laszlo Cseh is on course to win his first worlds gold medal for a decade as the fastest qualifier into the men's 200m butterfly final on Wednesday in 1:53.53.
But the world and Olympic champion Chad le Clos of South Africa is right behind him at 0.97 secs back in what promises to be a fascinating duel.
World records have now fallen on seven occasions in Kazan.
Sweden's Sarah Sjostrom broke the women's 100m butterfly record twice en route to winning gold in Monday's final in 55.64secs.
Hungary's 'Iron Lady', Katinka Hosszu, set a new record of two mins 06.12 secs when she won gold in the 200m individual medley final, also on Monday, before the exploits of Van der Burgh, Peaty and Ledecky.