Rio de Janeiro: Katie Ledecky obliterated the field and her own world record in winning the 800m freestyle at the Rio Olympics on Friday, uniting the 200m, 400m and 800m titles for the first time since 1968.

The 19-year-old American, who also won the 4x200m relay for four golds overall, touched in 8min 04.79sec, beating the previous record of 8:06.68 she set in Austin, Texas, on January 17 of this year.

Ledecky, who shot to prominence with her surprise victory in the 800m free in London four years ago, touched almost half a length in front of her closest rivals — silver medallist Jazz Carlin of Britain (8:16.17) and bronze medallist Boglarka Kapas of Hungary (8:16.37).

Ledecky joined compatriots Janet Evans and Brooke Bennett as the only swimmers to win this event at two Olympics.

She now owns the top 11 performances ever in the event.

Ledecky is also the first Olympian to take the 200m, 400m and 800m gold at one Games since another US teenager, Debbie Meyer, achieved the feat at Mexico City in 1968.