Katie Ledecky sliced 2.86sec off her 800m freestyle world record, clocking 8min 11.00sec at a meet in Texas for her second world record in four days.
The 17-year-old American on Sunday improved on her own previous 800m free world record of 8:13.86 set at the World Championships in Barcelona in August of last year.
On Thursday night, Ledecky had shattered her previous record in the 1,500m free with a time of 15:34.23, improving on the mark of 15:36.53 she had set in Barcelona.
Ledecky is the Olympic champion in the 800m free. The women's 1,500m free isn't contested in the Olympics, although it is a World Championships event for both men and women.
Ledecky is in strong form with the US Championships in Irvine, California, looming in August.
Those championships are a selection meeting for the Pan Pacific Championships in Australia later that month, as well as the 2015 World Championships in Russia.