Katie Ledecky (Getty Images)
Rio de Janeiro - Katie Ledecky of the United States crushed her world record in the 400m freestyle to win Olympic gold on Sunday and jump-start a potentially historic Rio campaign.
The American phenom - targeting a rare 200m, 400m and 800m Olympic freestyle treble - surged home to touch the wall in 3:56.46, smashing her own world record of 3:58.37 set in the Gold Coast, Queensland in 2014.
Ledecky, who has gone from strength to strength since her surprise win in the 800m freestyle as a 15-year-old in London, has now broken 12 world records since then.
"A goal I set after Barcelona in 2013 was 3:56 or better so to see 3:56 feels really good," said Ledecky, who beamed when she saw the time.
She had come 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. It just felt great."
Jazz Carlin of Great Britain won silver - her 4:01.23 leaving her 4.77 seconds adrift. American Leah Smith took bronze in 4:01.92.