BUDAPEST, Hungary -- Katie Ledecky led an American one-two and won her fourth 1,500-meter freestyle title at the world swimming championships Monday.
Ledecky never looked threatened and clocked 15:30.15 -- just under 10 seconds more than her world record from 2018 -- to finish 14.74 seconds ahead of Katie Grimes.
Ledecky punched the water in delight before waiting to embrace her teammate.
"To share this moment with her is really special,'' Ledecky said.
Grimes, 16, is the second-youngest medalist in the 1,500 at a worlds since Ledecky won it for the first time in 2013.
"I was really nervous leading up to it because it's my first world championships and Team USA has been doing a great job, so I wanted to keep that going,'' Grimes said.
Italy's Thomas Ceccon, meanwhile, set a world record in the men's 100 backstroke with a time of 51.60 seconds, shaving 0.15 seconds off the previous best mark set by American Ryan Murphy at the 2016 Olympics.
"Yesterday I swam 52.1, very easy,'' Ceccon said. "I am feeling good in water and just doing my race, staying calm and focusing on my race. And that's it.''
Murphy finished second, 0.37 seconds behind, followed by compatriot Hunter Armstrong, 0.38 behind Ceccon.
"Hats off to Thomas,'' Murphy said of seeing his record beaten. "That's a really, really fast time and it's going to be an exciting couple of years.''
Ceccon is the second Italian man to set a world record in long-course swimming after Giorgio Lamberti. Lamberti held the record in the men's 200 freestyle from 1989 to '99. Ceccon is also the youngest gold medalist at 21 in the men's 100 backstroke at a worlds since the then-19-year-old Aaron Peirsol of the United States won in 2003.
Ledecky also won in 2015 and 2017 and has at least four world titles in the each of the 1,500-, 800- and 400-meter freestyle events. The gold Monday was her record-extending 17th world title.
Only compatriot Michael Phelps also won at least four gold medals in three different swimming events at the worlds, though he achieved it in just one individual event -- five 200 butterfly titles -- as well as two relays (4x100 medley, 4x200 freestyle).
"I don't think that anyone will be topping Katie for a little while, but I definitely think it's a goal for everyone moving forward,'' said Australia's Lani Pallister, who finished third, 18.81 off Ledecky's pace. "She's definitely set the standard of distance swimming in the world.''
Pallister finished third, 18.81 off Ledecky's pace, for her country's first medal in this race. The 1,500 freestyle was the only women's event at a worlds in which an Australian swimmer had not reached the podium.
Italy's Simona Quadarella, who was second-fastest in qualifying, finished fifth, more than half a minute behind.
Regan Smith got another gold for the United States in the women's 100 backstroke, clocking 58.22 to finish 0.18 ahead of Canadian rival Kylie Masse with another American, Claire Curzan, finishing third.
Italy's Benedetta Pilato, 17, won the women's 100 breaststroke in 1:05.93, 0.05 ahead of Germany's Anna Elendt and 0.09 ahead of Lithuania's Ruta Meilutyte. Pilato, who couldn't contain her delight, is the youngest Italian swimmer to win gold at a worlds.
She brought her country's tally of golds to three, already as many as Italy's swimmers ever managed at a previous worlds.
Also, Romania's David Popovici set a world junior record to win the men's 200 meters in 1:43.21. Popovici, 17, was 1.26 seconds ahead of South Korea's Hwang Sun-woo and 1.77 ahead of Britain's Tom Dean.
The Associated Press contributed to this report.