Singapore: Mollie O’Callaghan has equalled Ian Thorpe for the most world championship gold medals by an Australian swimmer after anchoring the Dolphins to a stirring relay victory over the United States in the 4x200m freestyle final.

It was a case of no Ariarne Titmus, no worries for Australia, who recorded a narrow win by 0.66 seconds over the USA to pick up gold No.5 of the meet, and maintain top spot on the medal tally with three days of racing to go in Singapore.

On a night when Kyle Chalmers (100m freestyle) and Lizzy Dekkers (200m butterfly) added individual bronze medals, Australia was pitted against a star-studded USA team who, like in the 4x100 freestyle relay, had enough quality on its roster to topple the reigning Olympic champions.

Afterwards, the Australians admitted they didn’t think they could win and back up their gold medal from the Paris Olympics last year.

“Losing Arnie, we probably didn’t think we would win this event tonight,” said Lani Pallister, who opened with a personal best of 1:54.77 to give Australia an early lead. “Showing that we still have the depth, minus one, is wicked.”

The team of Pallister, Jamie Perkins, Brittany Castelluzzo and O’Callaghan held on to continue the USA’s relay woes at these world championships.

Gold medallists Lani Pallister, Jamie Perkins, Brittany Castelluzzo and Mollie O’Callaghan after winning gold in the women’s 4x200m freestyle relay.

Perkins (1:55.13) held firm in the second leg before Castelluzzo (1:56.01) resisted the urge to chase hard after Erin Gemmell, who had put the US ahead.

Castelluzzo delivered a composed swim to give O’Callaghan a 0.41 second lead going into the final leg against American great Katie Ledecky. Australia stopped the clock in 7:39.35, ahead of the USA in 7:40.01.

“I know my back-end is my strength, so I was just trying to keep calm and then have fun trying to mow someone down the last 50,” Castelluzzo said.

O’Callaghan, fresh from victory in the individual 200m freestyle, held her nerve against Ledecky – the Olympic champion in this event in 2016 – to secure her 11th world title and draw level with Thorpe.

Katie Ledecky and Mollie O’Callaghan after Australia’s relay victory.

“Without the profanities, I was pretty much saying to Mollie on the blocks, ‘Do you know who you are?’” Pallister said. “Even in my mind, as soon as Mollie dives in, I know we’d won it. I have so much confidence in her.

“Brit swimming as fast as she did, and Jamie as well ... I think it shows the depth that we’ve got going into LA.”

Typically humble, O’Callaghan tried to downplay the milestone, but acknowledged its significance after moving past Grant Hackett’s tally of 10 golds.

O’Callaghan, who is building a compelling case to be considered Australia’s greatest ever swimmer, could win a 12th gold medal on Friday night in the 100m freestyle after cruising through her semi-final.

“It is very special. It would be wrong if I said it wasn’t special. It is a huge accomplishment in a way,” O’Callaghan said of comparisons to Thorpe.

“It just shows the journey that I’ve had and us girls have had. I’ve got great girls to train alongside and they keep me on my toes.”

Chalmers ‘extremely proud’ of bronze in freestyle final

Meanwhile, Chalmers and Dekkers’ bronze medals were unique in their own way.

Chalmers, for a start, never comes third. This was his first individual bronze medal during a decade-long career.

A year after his silver medal in Paris, Chalmers (47.17) just couldn’t match it with Romania’s David Popovici (46.51) and USA national record holder Jack Alexy (46.92).

The ingredients were there for Chalmers to do something special given the sharp times he’s been clocking but Cameron McEvoy’s Australian record of 47.04 from 2016 remains intact.

“I was never going to swim 46.5 or around that mark unfortunately,” Chalmers said. “I would have loved to see 46 next to my name, but I’m really proud of that performance and to come away with a medal in such a stacked final is something I’m extremely proud of.”

Popovici’s winning time was just 0.11 seconds outside Pan Zhanle’s world record, set in Paris last year.

Asked what was next, the 20-year-old said: “To have a big holiday, go on the beach, lay on my back, celebrate accordingly, have some fun, get my motorcycle licence, learn to cook, drive my fast car and enjoy life a little because it’s not all about swimming.”

Dekkers’ bronze, meanwhile, was a surprise given she finished third in the event at trials and Australia only take the top two.

When Abbey Connor pulled out, Dekkers was given a second shot and didn’t disappoint, backing up her silver medal from the world championships two years ago after minimal training in recent months.

Lizzy Dekkers (right) with her bronze medal from the women’s 200m butterfly.

“It was definitely tough. I was on break and getting ready to not race for six months or so,” Dekkers said. “But at the end of the day, this wasn’t an opportunity I was going to pass up. The world champs don’t come around all that often, so I just got up and got ready and just put no expectations on it.”

Canada’s Summer McIntosh won the 200m butterfly and cursed at herself for not breaking the world record, while France’s Leon Marchand took out the 200m individual medley in a time of 1:53.68, but it wasn’t another world record.

With his favoured 400m IM still to come, Marchand appears to be keeping something in reserve as he eyes a historic sub-four-minute swim.

As for the Americans? Four gold medals in five nights is a bad return by their high standards.

Australia’s swimmers are living rent-free in their head at the moment.