Katie Ledecky claimed her 13th career world championship gold medal on Thursday as the USA ruled the pool in Budapest with a hat-trick of victories.

Ledecky led the USA to the women's 4x200m freestyle title with a powerful anchor leg to win her fourth gold medal in the Hungarian capital and the 13th world title of her career.

Ledecky sealed gold for the USA quartet, alongside Leah Smith, Mallory Comerford, Melanie Margalis, as she held off China's Li Bingjie, who took silver for China, while Adriane Titmus earned bronze for Australia.

"It was a big victory for us," said Ledecky.

It was the perfect response after the 20-year-old Ledecky was beaten into joint second in Wednesday's 200m freestyle -- her first defeat in 13 finals at world championships.

"I had no frustation about yesterday any more. I had confidence in my other team mates, that we can do it together."

Ledecky has now won five medals at these championships after gold in the 400m freestyle, 1500m freestyle, the 4x100m, plus that 200m silver.

Another gold beckons for her on Saturday night when she defends her 800m freestyle crown as the reigning world and Olympic champion.

Ledecky helped the USA quartet win gold after Chase Kalisz had earlier won the men's 200m individual medley gold.

He touched the wall at one minute, 55.56 seconds, with Japan's Kosuke Hagino taking silver at 0.45sec and China's Wang Shun earning bronze at 0.72.

- Phelps, Lochte legacy -

It means he follows in the footsteps of compatriots Michael Phelps, who won the 200m IM gold medal at four Olympic Games from 2004 until 2016, and Lochte, who won four titles in the event from 2009 until 2015.

"Those two are the best in our sport, they will never be replaced and it means a lot to continue the IM tradition -- they were my idols," said the 23-year-old.

Caeleb Dressel and Nathan Adrian came first and second respectively in the men's 100m freestyle final as the Americans dominated the podium.

"We're fine with the silver we're stoked to see team USA go one-two," said the 28-year-old Adrian.

Elsewhere at the Duna Arena on Thursday, Mireia Belmonte overcame a sore throat to win the women's 200m butterfly title to add to her Olympic gold medal.

The Spaniard touched the wall in two minutes, 05.26 seconds with Germany's Franziska Hentke taking silver at 0.13 back and Hungary's Katinka Hosszu earning bronze at 0.63.

Having won world silver at home in Barcelona four years ago, Belmonte has gone one better a year after being crowned Olympic champion in Rio.

- Fu's tears -

Brazil's Etiene Medeiros won the women's 50m backstroke final in a desperately tight final when the gold medal was decided by a single hundredths of a second.

Medeiros clocked 27.14 seconds, a new Americas record just 0.08 away from the world record set in 2009, while China's Fu Yuanhui took silver at 0.01 back.

Fu became a social media star at the 2016 Rio Olympics after a video of her smiling, having been told she had won joint bronze in the 100m backstroke, went viral as she struggled to contain her emotions.

But her tears of joy in Rio were juxtaposed by her bitter disappointment in Budapest at missing out on a gold medal.

"It is a heartbreaking result, I tried my best, I was swimming not just for myself but for my coach, my friends, my family," said the 21-year-old.

"People know me for laughing, but if they see me crying they will be very sad, so this time I will go home before I cry."

source: AFP