William Yang is also off to Paris after touching the wall in 48.08, ahead of Flynn Southam (48.11), Jack Cartwright (48.4), Kai Taylor (48.57) and Zac Incerti (48.73) who are all likely to be taken as relay swimmers.

Asked if he feared he wouldn’t be able to compete in Brisbane, Chalmers said: “For sure. It definitely hasn’t been easy. It’s been pretty hard. It was very stressful.

“I’ve put on a pretty brave face to be able to get through it, but it’s definitely been quite challenging just getting in and out of bed and starting the day. All I had to do was two laps in the swimming pool.

“It’s probably the most special one I’ve had to qualify for. I think because I’ve had to work so hard to get to this point. It hasn’t been given to me. I’ve had to fight back from injury, mental health, and a change of coach.”

Chalmers faces a difficult assignment to win Olympic gold after China’s Pan Zhanle lowered the world record to 46.8 earlier this year.

Australia’s richest woman, Gina Rinehart, was in the stands alongside Olympic great Dawn Fraser and Swimming Australia chief executive Rob Woodhouse to watch Chalmers and other swimmers in action.

Earlier on night four of action, Kaylee McKeown capped off a near perfect Olympic trials by securing victory in the 200m backstroke – her third win in as many races.

After victories in the 200-metre individual medley and 100m backstroke over the previous three evenings, McKeown continued her clinical run with victory by more than four seconds.

McKeown, the world record holder in this event, took an early lead like she does so often before blowing the field away in a time of 2:03.3 – an ominous sign for her rivals ahead of next month’s Olympics.

She was under world record pace by 0.15 seconds at the 100-metre mark before narrowly missing her lifetime best by 0.16 seconds.

“The first half of this meet I’ve been quite nervous, so I really just wanted to enjoy tonight, so I’m glad you could see that on camera,” McKeown said on Channel Nine. “I didn’t hear anything, I was in my own little world, but I’ve got a ticket to Paris, so I’m hoping to be on the big stage for that.

“I lost my dad in 2020 to brain cancer just before the Olympics, so every swim that I do he’s always there with me.”

Meanwhile, Jaclyn Barclay is off to her first Olympics after clocking a time of 2:07.88, ahead of Hannah Fredericks (2:08.25) in third.

Emily Seebohm’s bid to qualify for a fifth Olympics – no Australian swimmer has gone to more than four – ended in disappointment after her fifth-placed finish in a time of 2:10.8.

Seebohm, a bronze medallist in this event at the Tokyo Olympics, had a child last year and was aiming to become the first mother to make Australia’s Olympic swimming team since Hayley Lewis in 2000.

McKeown’s biggest rival in the 200m event in Paris will be American star Regan Smith, who owns the second and third-fastest times in history.

Smith finished second to McKeown in the 50m, 100m and 200m backstroke events at last year’s world championships in Fukuoka.

The 22-year-old from Minnesota will be in the water at the USA trials in Indianapolis next week, when Australia’s swimmers and coaches will get an important gauge of where they are sitting in the pecking order before Paris.

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Ariarne Titmus took out the 800m freestyle in 8:14.06, ahead of Lani Pallister, but said she wasn’t happy with the time.

“I won’t get in trouble too much now knowing that at least I put myself out there,” Titmus said. “I’m disappointed with the time. I know I’m better than that, but at least I get the chance to do it again at the Olympics.”

Elsewhere, Lizzy Dekkers and Abbey Connor qualified for their first Olympics in the 200m butterfly, while Will Petric narrowly missed Swimming Australia’s qualifying time.

“Yeah, it’s annoying, but you know, Swimming Australia’s always had tremendous success overseas and the qualifying times must have something to do with it,” Petric said. “I don’t want to go there and not make a final.”