Rio de Janeiro (AFP) - "Pure happiness" radiated from Katie Ledecky as the 19-year-old us freestyle phenom gazed at the scoreboard and contemplated her latest feat: 400m free Olympic gold in world record time.
Ledecky, targeting a rare 200m, 400m and 800m Olympic freestyle treble -- surged home to touch the wall in 3min 56.46sec, smashing her own world record of 3:58.37 set in the Gold Coast, Queensland in 2014.
Upon seeing her time, she grinned broadly having achieved a goal she'd set herself back in 2013 of lowering the record in the event to "3:56 or better".
"To see 3:56 feels really good," said Ledecky, who now owns the six fastest times ever in the event and is one of only two women even to break four minutes.
Italy's Federica Pellegrini did it twice, in the era of the now-banned supersuits.
Ledecky, who has gone from strength to strength since her surprise win in the 800m free as a 15-year-old in London, has broken 12 world records since then.
On Sunday, she covered the last 50m in a blazing 28.92sec, leaving Jazz Carlin of Great Britain to collect silver in 4:01.23 -- 4.77 seconds adrift. American Leah Smith took bronze in 4:01.92.
"I just let it all out," said Ledecky, who came within a whisker of the world mark in the afternoon heats, clocking 3:58.71 -- the second-fastest ever until her gold medal swim.
"It felt pretty identical to this morning, with a little more pop on the back half," Ledecky said. "It just felt great."
Smith, who was thrilled to finish less than two seconds behind Ledecky in the 400m free at the US trials, said she knew Ledecky was primed for something big.
"I've been training with her for the past month," Smith said. "So I knew it was coming. It was only a matter of how fast she was going to go."
Next up for Ledecky is the 200m free, which starts with heats and semi-finals on Monday, with the 800m free on Friday.
She could become the first woman since Debbie Meyer in Mexico City in 1968 to sweep the 200m, 400m and 800m free at the Games, and will be a contender with the US team in the 4x200m free.
If Ledecky wins her remaining events, she'll become just the third US woman, after Amy Van Dyken in 1996 and Missy Franklin in 2012 to win four gold medals in a single Olympics.
Ledecky anchored the 4x100 free team that set a US record and earned silver behind Australia on Saturday