Then the 15-year-old schoolgirl went out and won her own gold medal.
Ledecky touched first in the 800-meter freestyle with a time of 8 minutes, 15.63 seconds on Friday night, beating a field that included defending Olympic champion Rebecca Adlington of Britain and 2008 bronze medallist Lotte Friis of Denmark.
"I didn't really expect gold, but I'll take it," Ledecky said, smiling.
She lowered Janet Evans' American record of 8:16.22 set on Aug. 20, 1989 — eight years before Ledecky was born.
Already the youngest swimmer on the U.S. team, Ledecky became the second-youngest American woman to win an individual gold medal.
Beth Botsford was 15 years and 62 days when she won the 100 backstroke at the 1996 Atlanta Games; Ledecky is 15 years and 139 days.
"To break that record is really cool and really special," she said about Evans' mark.
Evans tweeted out her congratulations to Ledecky after the race: "Amazing swim, so proud of her for bringing distance gold back to the US!"
Ledecky described Evans as someone she's looked up to, having watched her races on the Internet. Evans won the 800 free at the 1988 Seoul Olympics — as a 16-year-old — and again in 1992 in Barcelona.
"They're really neat to watch," she said.
Ledecky is the first U.S. woman to win the event since Brooke Bennett picked up where Evans left off in winning back-to-back titles in 1996 and 2000.
"Welcome to the gold medal club," Bennett tweeted to Ledecky. "That was incredible to watch."
Ledecky seemingly came out of nowhere to claim a spot on the U.S. team, and she nearly took out a world record in her first Olympics. She was ahead of Adlington's record pace (8:14.10) from the Beijing Games until the last 15 metres of a race she thoroughly dominated.
"She was absolutely amazing," said Adlington, who settled for bronze in 8:20.32. "That time is unbelievable. She has got a bright career ahead of her."
Mireia Belmonte Garcia of Spain took the silver in 8:18.76.
Ledecky watched Franklin and Phelps win gold medals before her only race of the games.
"I got really pumped up when I saw that Missy and Michael had really good swims," the youngster said. "I was ready to scream when I saw Missy's race, but I kept it to myself and used it as extra energy."
Ledecky dropped 5.15 seconds from her time of 8.19.78 at last month's U.S. trials, when she broke the trials record and won by 2.09 seconds. She just missed making the team in the 400 free, having broken Evans' national age group record while finishing third.
"My game plan has always been go out fast but not too fast because it'll affect me later on in the race," Ledecky said about her Olympic win. "I tried to go out a little more controlled, but I just got so excited and started racing. I've been working on that back half so I was able to come home hard."
Ledecky's big time drop combined with questions about the use of performance-enhancing drugs directed at 16-year-old Ye Shiwen of China after she won two golds at these games prompted a reporter to ask the American if she was cheating.
"It's totally false," Ledecky answered calmly. "I just put in a lot of hard work this past year. Just progressively setting short-term and long-term goals. I've been dropping time progressively."