RIO DE JANEIRO - Four years ago, Katie Ledecky stunned the world with her breakout performance in the women's 800m freestyle at the London Games.
On Friday, expectations for the bona fide superstar could not be more different. The 19-year-old American was tipped to obliterate the field and she did, retaining her Olympic title in a world record time of 8min 4.79sec.
She was 11.38sec - or almost half a pool-length - ahead of silver medallist Carlin Jazz of Great Britain.
Hungary's Boglarka Kapas took bronze (8:16.37) at the Olympic Aquatics Stadium.
Ledecky now owns the 13 fastest times ever in the 800m free. Since stopping the clock at 8:13.86 in London, she has broken the event's world record five times.
Her latest mark eclipses her own record of 8:06.68 - set in Austin, Texas in January.
It is also over nine seconds lower than the anyone in history, with Great Britain's Rebecca Adlington posting 8:14.10 to become the world record holder in 2008.
"I had a lot of fun tonight," Ledecky said. "I just wanted to push myself and see what I could do."
Ledecky has yet to lose an individual final at the Olympics or world championships in 11 races.
She is the third American female swimmer after Amy Van Dyken (1996 Atlanta Games) and Missy Franklin (2012) to win four golds in a single Olympics.
She won 400m free gold in world-record time on Sunday, 200m free gold on Tuesday, then anchored the US' 4x200m free relay team to victory a day later.
The only other female swimmer to complete the 200m, 400m, and 800m treble was compatriot Debbie Meyer 48 years ago.