Swim stalwarts Kyle Chalmers and Emma McKeon can scarcely believe Australia’s glorious opening night at the pool at the world championships in Japan.

Two world records. Four gold medals from five on offer.

Chalmers: “I sat there with goosebumps all night.”

McKeon: “Two world records. Four golds. It’s just, like, nuts.”

Ariarne Titmus reclaimed her women’s 400m freestyle record.

Australia’s 4x100m freestyle relay team – McKeon, Mollie O’Callaghan, Meg Harris and Shayna Jack – broke the world record their nation set at the Tokyo Olympics of 2021.

They finished in three minutes 27.96 seconds, well inside the previous high water-mark of 3:29.69.

Sam Short (400m freestyle) and Australia’s men’s 4x100m freestyle relayers – Jack Cartwright, Flynn Southam, Kai Taylor and Kyle Chalmers – also saluted on Sunday night in Fukuoka.

Tweet from @DolphinsAUS

Chalmers: “I have been on world championships teams where we have probably struggled to win four medals for the whole competition, let alone four gold medals on the first night.”

Short set the tone with victory in the men’s 400m freestyle, the first final of the meet.

McKeon: “I was in the call room for my 100 ‘fly semi when Sam was swimming. And you get the goosebumps all through you – to have people swimming that quickly for your team just lifts your team up.”

Chalmers: “Shorty … we have sat there for the last two weeks watching him dominate training and talk the big game. And for him to deliver was that spine-tingling moment.”

Next came Titmus’ astonishing feat, blitzing her chief rivals, American legend Katie Ledecky and Canada’s 16-year-old star Summer McIntosh in a match race between a trio who had all held the world record in the past 18 months.

Titmus led from go to whoa, clocking 3:55.38 seconds, bettering McIntosh’s world mark of 3:56.08 set last March.

Titmus: “I honestly didn’t think about getting the world record back, it wasn’t something that I had my mind on for this meet at all. I just wanted to come here and try and swim the way I felt I was capable of swimming – and it was obviously enough to get the record back.”

Chalmers: “(For) Ariarne to break a world record and then the (relay) girls break a world record, I don’t think Australia could ask for a better night.”

The only gold the Aussies missed was because of a near superhuman swim from Leon Marchand in the men’s 400m individual medley.

The French star broke swimming’s longest-standing world record, eclipsing Michael Phelps’ mark of 4:03.84 from the 2008 Olympics – Marchand touched in 4:02.50.

— AAP