Katie Ledecky beat her own world record to win the 800m freestyle at the Pro Swim meeting in Austin, Texas.
The American, 18, touched home in eight minutes 6.68 seconds to smash the previous record of 8:07.39 set at the 2015 World Championships in Russia.
"It's exciting when you can get pushed along by a crowd like this," she said.
Michael Phelps, 30, won the 200m individual medley to notch his first win over rival Ryan Lochte in the event since the 2012 London Olympics.
Phelps, whose record 18 Olympic gold medals include three in the 200m individual medley, won in one minute 58.00 seconds.
Fellow American Lochte, the world record-holder in the event, held a narrow lead at every turn but lost the lead in the freestyle finale and finished second in 1:58.43.
"We have a couple more meets before the Olympic trials. Hopefully I'll be better than this," said Phelps, who came out of retirement in 2014 in a bid to reach his fifth Olympics and add to his record haul of gold medals.
Ledecky, the youngest member of the US Olympic delegation in London four years ago, now owns the eight fastest performances ever in the 800m free and nine of the top 10.
She also holds the world record in the 400m free and the non-Olympic women's event of 1500m free.