Katie Ledecky broke her 400m freestyle world record while Michael Phelps won gold for the first time since London 2012.
Ledecky won the Pan Pacific championships 400m title in three minutes, 58.37 seconds.
Ledecky was under world record pace for much of the race in an outdoor pool at the Gold Coast Aquatic Centre and finished strongly to shave almost a half-second off the mark she set at the US nationals earlier this month.
The 17-year-old Ledecky also holds the world records in the 800 and 1,500 freestyle events, and narrowly missed improving her mark in the 800 earlier at the Pan Pacs.
It was her fourth gold medal of the meet, following her titles in the 200, 800 and the 4x200-meter relay.
Meanwhile, Phelps, the most decorated swimmer in history won the 100m butterfly in 51.29, edging long-time US teammate Ryan Lochte.
This followerd the 29-year-old Phelps relay gold a day earlier as he won his first individual title since returning to international competition following a one-and-a-half-year retirement.