But the Australian powerhouse still reckons he's not the finished product.

Chalmers produced a personal best time of 47.48 seconds to win the national 100m freestyle title in Adelaide on Monday night.

His time was 0.10 seconds quicker than his gold-medal swim in the event at the 2016 Rio Olympics - his previous personal best.

And, despite being in heavy training, he now holds the two fastest times over the distance in the world this year.

"The whole race felt strong, I felt like I built through it pretty well ... so happy with that," Chalmers said.

"But I know that there's definitely areas to improve on.

"My skills are still things that are lacking and not world class yet.

"And I know if I can drop those 0.1 of a second, everything adds up.

"There's not many things that I want to change but there's probably those few things that are going to come with taper and swimming that bit faster in training."

Chalmers' feat came as Australia unearthed an accidental Commonwealth record holder in breaststroker Matthew Wilson.

Wilson broke the Commonwealth 200m breaststroke record in winning the Australian title.

The 20-year-old New South Welshman was stunned when he surfaced and saw his time - two minutes 07.16 seconds; 0.14 seconds quicker than the previous Commonwealth benchmark.

"I had no idea ... it just happened," Wilson said.

"A week ago I had a grade one hamstring strain so we didn't even know if I could swim here.

"It's kind of like an accidental taper ... I definitely didn't target this meet for a drop in time like that."

Wilson, who studies exercise and sports science at university, sheepishly admitted how his injury happened.

"It was a swimming injury - I'm probably the first swimmer ever to blow a hamstring doing swimming," he said.

"It got a bit tight and the next morning it was very hard to walk."

Wilson bettered Scotland's Ross Murdoch's previous Commonwealth benchmark by 0.14s which had stood for almost five years.

Australian Associated Press