KAZAN, Russia (AP) There's no stopping Katie Ledecky. The 18-year-old American virtually raced herself at the world swimming championships, and she was unbeatable.
Ledecky ended her meet in spectacular style Saturday night, lowering her own world record by 3.61 seconds in the 800-meter freestyle for her fifth gold medal.
She swam the 16-lap race in 8 minutes, 7.39 seconds, bettering her time of 8:11.00 set last year on home soil.
''I knew that I was capable of going sub-8:10,'' she said, ''so to go 8:07 means a lot.''
Ledecky completed a sweep of the 200, 400, 800 and 1,500 freestyles in Kazan. She swam the anchor leg on the victorious 4x200 free relay, too.
''It's really neat to say that you've done something nobody has done before,'' Ledecky said. ''I'll enjoy this for a few days and then I'll get back to work and hopefully there's more to come.''
She improved her results from two years ago in Barcelona, where she won four golds and set two world records. In Kazan, she won the 400 by 3.89 seconds, the 800 by 10.26 seconds and the 1,500 by 14.66 seconds, taking down her old world record in the preliminaries and the final.
Her closest race was the 200 free, when she rallied from fourth to win by 0.16 seconds.
''It could have been really tiring and it was,'' Ledecky said. ''But I recovered very well. I did what I needed to do to set myself up well each time that I got up on the blocks. I'm just proud of how I handled my races and how all this week has gone.''
On the men's side, Sun Yang of China is poised for a nearly similar feat. He won the 400 and 800 freestyles and is favored to add the 1,500 on the last day Sunday. Sun finished second in the 200 free by 0.06 seconds.
Ledecky was under world-record pace throughout the 800, leaving the other swimmers trailing well behind her wake. She tore off one of her two swim caps and smashed the water with her hand in celebration of her third world record in Russia.
''I really love to see what she can do,'' said Lauren Boyle, the silver medalist from New Zealand. ''It shows what is possible for the human body. It's very inspiring for me.''
Chad le Clos defended his title in the 100 butterfly, rallying late to edge Laszlo Cseh of Hungary in the absence of Olympic champion Michael Phelps, who beat Le Clos in London three years ago.
The South African was second at the turn and then poured it on down the stretch, touching in 50.56 seconds. Cseh was second in 50.87.
Le Clos slapped the water with his right hand, then pounded his chest and nodded his head as if to say yes. His father frantically urged him on from the stands, bellowing when his son got to the wall first.
About eight hours later, Phelps responded by beating Le Clos' time to win the 100 butterfly at the U.S. national championships in Texas. His time was 50.45 seconds, nearly a second faster than his gold-medal winning time in London.
Phelps has missed the last two worlds, and Le Clos has emerged as the fly king in his absence. The American qualified for the meet in Kazan, but was forced to sit out as a result of his suspension by USA Swimming for a second drunken driving arrest.
''I'm just very happy that he's back to his good form, so he can't come out and say, `Oh, I haven't been training' or all that rubbish that he's been talking,'' Le Clos said. ''I'll relish the opportunity to race him again.''
Phelps said he saw Le Clos' taunts from halfway around the world.
''There are a lot of things I could say. But I won't,'' Phelps said. ''I'm going to let what I do in the pool do my talking.''
Le Clos was coming off a disappointing second-place finish in the 200 fly behind Cseh, who has emerged as a medal threat for next year's Olympics with a resurgence in Kazan.
Florent Manaudou of France won the 50 free to go with his Olympic title. His time of 21.19 is fastest in the world this year.
Nathan Adrian of the United States finished second in 21.52. Bruno Fratus of Brazil took third.
Three-time defending champion Cesar Cielo of Brazil left Kazan earlier in the week because of a shoulder injury.
Defending champion Missy Franklin faltered in the 200 backstroke. She was overtaken down the stretch by Emily Seebohm of Australia, who touched in 2:05.81 to complete a sweep of the backstroke events.
The men's 100 and 200 back titles went Down Under too, with Seebohm's teammate, Mitchell Larkin, claiming both in a double that inspired Seebohm.
Franklin, the Olympic champion, settled for silver in 2:06.34. In seven events so far, Franklin has five medals, but no individual gold two years after she won a record six golds in Barcelona.
''This is probably one of the hardest races to get second, just because I love it so much,'' Franklin said. ''But I'm honestly really happy with that. I fought my heart out. I went out after it and I swam it like Missy Franklin swims a two backstroke. I'm just not there at the end yet, and that's all right.''
Katinka Hosszu of Hungary finished third.
Franklin returned later to anchor the U.S. team to victory in the mixed 4x100 free relay. Ryan Lochte, Adrian, Simone Manuel and Franklin won in 3:23.05, a world record. The Netherlands was second and Canada third.
Sarah Sjostrom of Sweden won the 50 butterfly, a non-Olympic event, in 24.96.
AP National Writer Paul Newberry contributed to this report in San Antonio.