The 17-year-old finished almost half a minute ahead of her nearest rival – an almost unimaginable margin in a sport where medals are often decided by hundredths of seconds – to collect her fifth title of the championships.
Ledecky broke her 400m world record on Saturday and came within a whisker of eclipsing her 800m world best on Thursday.
She also won the 200m individual event and anchored the United States to victory in the 4x200m to emerge as the biggest winner of the four-day meet at Australia’s Gold Coast.
“That was probably one of my most painful races, I don’t know whether to throw up or not,” Ledecky told reporters.
“But it paid off in the end. Pretty early on it felt like I was on world record pace.
“I was pretty sure I had it. Still, six seconds is
Ledecky’s performances have caught the eye of Phelps, who said: “She’s a stud. Watching her swim, it’s remarkable.”
Phelps picked up his third gold medal of the meet when he helped the U.S. win the men’s 4x100m medley relay after he was surprisingly beaten in the 200m individual medley, an event he had won at the last three Olympics before his short-lived retirement after London 2012.
Still struggling to find his best, Phelps was touched out by Japan’s Kosuke Hagino, who got his hand on the wall first in 1:56.02 to claim his second gold after also winning the 400 IM.
Asked about his week after signing off with gold in the medley relay, Phelps said in a pooldeck interview that it had been “up and down” but added “there’s no better way to end a great week of racing then being with these guys and finishing with a win.”
Phelps, once the master of winning tight races, finished just 0.02 behind Hagino while his team mate Ryan Lochte was left wondering what might have been after he took it too easy in the morning heats and failed to qualify for the final.
Lochte won the consolation final in the same time as Hagino won the main event to join Phelps in the American team for next year’s world championships in Russia, but didn’t get a medal.
Japan also won both 200m breaststroke finals with Yasuhiro Koseki taking out the men’s race and teenager Kanako Watanabe clinching the women’s.
Brazil claimed their first win of the championships when Bruno Fratus won the men’s 50m freestyle sprint in 21.44 while Canada also picked up their first when Ryan Cochrane won the men’s 800m title.
Australian sprinter Cate Campbell collected two more titles to finish the meet with four golds. She edged out her younger sister Bronte to win the 50m dash then anchored the host-nation to win the women’s medley relay.
(Reporting by Julian Linden in Singapore; editing by Josh Reich)