Olympic gold medallist Zac Stubblety-Cook smashed the World Record in the Men's 200m breaststroke final at the Australian Swimming Championships in Adelaide.

His time of 2:05.95 was 0.17 seconds under the old record held by Anton Chupkov of Russia, making him the first man in history to break the 2:06 barrier.

Stubblety-Cook won gold in the event at the Tokyo Olympic Games.

"I always had the goal in the back of my mind to be the first guy to go 2:05 and you don't get many opportunities and tonight was one of them," he said after the race

"Doesn't feel real yet, hasn't really sunk in. Probably sink in over the next few days, still got a few jobs to do before then."

"I was obviously hoping to swim fast and hoping to swim close to my best and that's just something else."

Stubblety-Cook said he was driven by process, not outcomes.

"I've thought about it and tried to be around that process but never kind of be like yeah, that's it, like I want to break a world record, but you know it happens," the understated swimmer said.

Matthew Wilson, who finished third, led out the race in fast time, allowing Stubblety-Cook to power home.

"Felt pretty good at the hundred so I knew I could bring it home, but yeah, I didn't think we were going fast."

'You can't make me out to be the villain': Chalmers could swim in World Championships after all

Earlier, Olympic freestyle gold medallist Kyle Chalmers dropped a bombshell, saying he is considering swimming at the World Championships, which would deprive pop sensation Cody Simpson of a spot on the team.

Chalmers opened up to the media about the physical and mental pain he has suffered in recent months after winning the Men's 50m butterfly event at the Australian Swimming Championships in Adelaide.

On Wednesday, Chalmers came second and Simpson third in the 100m butterfly, behind Olympian Matthew Temple.

Chalmers had previously said he was not going to swim at the World Championships in Budapest this June.

That decision opened the door for Simpson's incredible comeback to the pool after pursuing a successful, decade-long career in music.

But Chalmers says his form has surprised him and butterfly swimming is his first love, prompting a re-think about the World Championships.

"Well, you can't make me out to be the villain, right," Chalmers said if he does decide to compete, potentially robbing Simpson of a spot.

"Unfortunately, I started out as a butterflyer and I've been swimming, I've been on the team now for 8 years, I've watched the 100 butterfly from afar and always wanted to do it, my body hasn't allowed me to do it to this point," he said.

"For me, I have to have a serious sit-down with my coach [Peter Bishop] and my team around me and have that discussion over the next couple of days," he said when asked if he would swim in Budapest.

"Personally I think it's [swimming at the World Championships] going to be the best thing for me moving forward because I know my coach, my squad go to Europe, I'll be left here by myself training by myself," he said.

"Obviously I look at my preparation eight weeks ago, I wasn't in the pool at all, potentially not going to swim at all this year, potentially maybe never swim again

"My shoulders were in a whole lot of pain.

"I've given everything I possibly can to this sport over this past five-year period, mentally, physically, emotionally and was just extremely burnt out."

He said a holiday to Noosa with a friend prompted him to decide that if he was going to swim again, he would do the butterfly.

"Just to take that pressure and expectation of myself," he said.

"It's been a quick progression. I think it would have been very disrespectful for myself to stand there eight weeks ago and say I'm going to be at the World Championships swimming butterfly."

'It's about becoming comfortable being uncomfortable'

He said the final decision on swimming at the World Championships would be made with a view to the 2024 Olympic Games.

"I want to swim butterfly long course, I want to swim the 100 butterfly in Paris," he said.

Chalmers opened up about the enormous pressure he said he'd been feeling recently, saying he told his coach recently that he just wanted to go home.

"Every time I stand behind the blocks, there's so much pressure and expectation on me — obviously the media doesn't help that either — I can't just do my own thing and race how I want to do now," he said.

Asked why he keeps going after enduring so much physical pain from multiple shoulder operations as well as mental anguish he replied: "What else do I have?"

"You do it for the love of it."

"I've gone through so much physical pain especially over these last two and a half years."

He revealed he recently ripped some bone off his ankle.

"For me it's about becoming comfortable being uncomfortable," he said.

"It's about dealing with these issues, dealing with the injuries, dealing with the setbacks — the mental side of things.

"People like to look at us as perfect humans but unfortunately we're the same as everyone else … we're not some robots.

"It's not just train and have fun and enjoy it, it's a whole lot of physical, mental and emotional setbacks to get to that point and it's why I love racing."

The triple Olympic gold medallist, Kaylee McKeown also had a revelation after winning the 400m Individual Medley in a world class time of 4:31.74.

McKeown won two individual backstroke gold medals as well as a relay gold medal in Tokyo but has revealed she'd probably swim the 400 IM at the World Championships as well as her pet strokes — the 100m and 200m backstroke.

"It's definitely going to be a hard year to kind of choose what I'm going to do and at the same time it's the year to do it," she said.

McKeown said her coach (Michael Bohl) would allow her to make the final decision on whether to swim the 400m Individual medley

When pushed on whether she wanted to, she replied: "Do I? No, but will I? Yes."