Katie Ledecky smashed another world record as Michael Phelps claimed his first individual gold medal post-retirement at the Pan Pacific Championships in Australia on Saturday.
American wonder teen Ledecky set the first world record of the Gold Coast meet, shaving almost half a second off the 400-metres freestyle mark she set at this month's US Championships.
The 17-year-old schoolgirl clocked three minutes 58.37 seconds to eclipse her previous mark by 0.49sec.
"It's a great feeling. It never really gets old," Ledecky said of her latest world record-breaking swim.
"I knew I could be right where I was at nationals, or slightly better. I'm really pleased with that."
While it was Ledecky's fourth gold medal of the championship, it was Olympic legend Phelps's second win but his first individual gold in taking out the 100m butterfly from rival teammate Ryan Lochte.
Phelps, 29, who was a member of the USA's winning 4x200m freestyle relay Friday, shaded Lochte by 0.38sec in winning the butterfly event in 51.29 adding to his haul of international titles just four months into his comeback.
"It's definitely feels good to have that sort of confidence back to be able to do it in an individual event," said Phelps, who has now won 15 golds over four Pan Pacs meets.
"What it does is guarantee me a spot on the world championship team next summer which is the biggest and most important thing.
"I know there is a lot can happen in a year with training, I'm looking forward to it, it's a building year for me."
Phelps, the 18-time Olympic champion, said he still has a few things to iron out after ending a near two-year retirement after the London Olympics.
- 'Really nail it' -
"After just getting back in the water and going through the ups and downs, it's still some of the small things like hitting the walls like I want to at a high speed," he said.
"That's something that I have to work on over the next year and really nail it."
Ledecky holds the world records in the 400m, 800m and 1500m freestyle to make her the first woman since US distance great Janet Evans to hold all three records at the same time.
Ledecky's win in Saturday's 400m final was her fourth gold medal of the Pan Pacs after wins in the 200m and 800m freestyle and as part of the USA 4x200m freestyle relay.
"I have some long-term goals. We're not quite there yet, but we'll get there," she said.
Ledecky still has the 1500m freestyle event to come on Sunday's last day of the Gold Coast meet as she chases five gold medals.
South Korea's Park Taeh-wan won his third consecutive Pan Pacs 400m freestyle title with victory over Japan's Kosuke Hagino. Olympic silver medallist Park's time was 3:43.15.
Commonwealth Games champion Belinda Hocking won the 200m backstroke, Australian teammate Alicia Coutts took out the 100m butterfly and American Tyler Clary captured the men's 200m backstroke final.
Hosts Australia won both 4x100m freestyle relays beating the United States.
The women's team, comprising world champion Cate Campbell, Brittany Elmslie, Melanie Schlanger and Bronte Campbell, won the final in a new meet record of 3:32.46.
Australia's men -- Tommaso D'Orsogna, James Magnussen, Matthew Abood, Cameron McEvoy -- prevailed over the Americans, which included Phelps, Nathan Adrian, Anthony Ervin and Lochte, by 0.56sec in a winning time of 3:12.80.
Heading into Sunday's final day of the meet, the USA has 11 gold, Australia eight, Japan four and South Korea one.