RIO DE JANEIRO -- Katie Ledecky set an Olympic record Sunday in her preliminary heat of the women's 400-meter freestyle, falling 0.34 seconds shy of her own world record with a time of 3:58.71.
Ledecky said after posting the second-fastest time ever that she purposely took it out "easy."
"I didn't want to spin my wheels too much, so I just kind of backed off and kept it easy up front," she said. "I know that's how I swim my 400 the best when I can be strong at the end."
In Sunday night's final, Ledecky will chase the 3:58.37 she posted two years earlier at Pan Pacific Championships in Australia.
"I know what my times are, and I have my goals," she said.
The next-fastest qualifier was Britain's Jazz Carlin, who was more than 4 seconds behind. American Leah Smith posted the third-fastest time in the prelims.
Before the prelims, the first individual event of Ledecky's Rio Olympics, her coach, Bruce Gemmell, offered a word of warning to the 19-year-old American.
"He had to remind me this wasn't a hundred," Ledecky said.
The issue had never been something Gemmell had to worry about before. But that changed after Ledecky swam the anchor leg in the final of the 4x100 freestyle relay late Saturday night. Yet she didn't appear to show any lingering effects from that race.
Ledecky said she didn't get to bed until around 2:45 a.m. local time. After interviews, a warm-down swim and a massage, she stayed to eat at the Aquatics Center with food prepared by one of her favorite chefs from the U.S. Olympic Training Center in Colorado Springs, Colorado. She said she slept until around 11 a.m. before heading to the pool for her 400 free prelim.
In that race, she was 0.64 seconds behind her world-record pace at the halfway point before narrowing the gap to 0.03 seconds with 50 meters to go. As the raucous Brazilian crowd cheered her on, Ledecky couldn't quite finish the job.
On Sunday night, the result could be different.
"That's the easiest it's felt in the 400, so I'm excited for tonight," she said.
The Associated Press contributed to this report.