On a day when the most decorated athlete in Olympic history etched yet another golden chapter into his growing legend in the pool, a pair of talented newcomers showed the future of United States swimming is in mighty good hands.

With a furious final sprint in the 100-meter butterfly, Michael Phelps won his fourth gold medal of the London Games and the 17th of his illustrious career.

The race, which Phelps has said would be his final individual Olympic event at his final Games, was bracketed by a pair of jaw-dropping performances from two teenagers who appear more than ready to take up the mantle for their country.

Missy Franklin, the bubbly 17-year-old who charmed the nation with her gold medal swim in Monday’s 100-meter backstroke, doubled her individual haul with a record-smashing swim in the 200 back.

But the biggest splash of the night was provided by a 15-year-old Katie Ledecky, a first-time Olympian from Bethesda who annihilated the field in the 800-meter freestyle. Ledecky led from start to finish and despite narrowly missing out on a world record time; her 8 minutes 14.63 seconds was more than four full seconds better than Spain’s Mireia Belmonte Garcia who won silver in 8:18.76.

“At one point I thought I could be close to the world record,” said Ledecky, who was named All-Met as a freshman at Stone Ridge this past winter. “[Then I thought,] ‘I don’t even care, just get to the wall first.’”

Phelps’ defense of his two previous gold medals in his event was a bit more dramatic.

The 27-year-old Baltimore native was in seventh place at the turn but quickly made up ground and ended with a flurry to post a time of 51.21. South Africa’s Chad le Clos — who denied Phelps a third straight gold in the 200 butterfly — finished second in 51.44 and Russia’s Evgeny Korotyshkin took bronze (51.44). American Tyler McGill finished seventh.

One day after becoming the first man to win gold in the same individual swimming event at three consecutive Olympics, Phelps became the first to accomplish the feat twice.

“I don’t even want to complain about going slower, having a bad touch or finish,” Phelps said. “I’m not even going to say any of that; I’m just happy the last one was a win.”

Franklin’s time of 2:04.06 seconds was nearly two seconds faster than Russian silver medalist Anastasia Zueva (2:05.92.). The gold is her third of these Games and fourth overall. In addition to her gold in the 100 back, Franklin helped the women’s 4x200 freestyle relay team to gold and took bronze with the 4x100 freestyle team.

“I just wanted to go out and do my best and get a best time,” Franklin said. “It just so happened to be a world record so I couldn’t be happier.”

The U.S. has now won 42 medals in London, 23 of them in the pool, and there likely will be more to come. Jessica Hardy will swim Saturday’s women’s 50-meter freestyle final, and the United States also will compete in Saturday’s men’s and women’s 4x100-meter medley relay finals.

Amy Shipley contributed from London.