And to claim the win in an equal fastest time in the world this year of 52.69 seconds, the 22-year-old Queenslander had to fend off a mighty challenge from her younger sister Bronte, 20, who led at the 50-metre mark but was left to finish second in 53.04.

Finishing in third place was another Queenslander, Melanie Wright, in 53.50.

"I am absolutely thrilled," said an exhausted Cate Campbell after exiting the Sydney Olympic Aquatic Centre pool at Homebush.

"Bronte was always going to make that very tough for me, and she absolutely was. She swam like an absolute champion.

"I have to give her a lot of credit. She is there by my side every step of the way. I wouldn't be the swimmer I am without her and without Simon [Cusack] my coach."

Cate said she was especially satisfied with her victory, considering it came despite missing eight weeks of training due to shoulder surgery that left her with only three months to train.

"I'm very, very happy with that," she said. "It was a smart swim more than anything else.

"I used every bit of the training I had done and that's what got me that time.

"I wasn't rushed, did everything that I had been practising in training."

Asked if she had intended to stick with her sister and finish strong, Cate said: "I was just swimming my own race … I am usually out kind of first.

"So I try not to look around too much because, technically speaking, my back end isn't the best in the world.

"If I turn and see someone there I could get a little bit scared.

"So I just swam my own race and made sure I attacked all the things that I needed to attack."

Cate said she knew that she would have to push through the pain barrier on the return lap.

"I knew I was in mega pain, but you've just got to embrace it," she said.

"That's my goal [in] this prep … to teach myself to love the sting, to reprogram that brain to not shy away from that but to embrace it."

Despite her equal best in the world for the year so far, Cate believes she will have to lift for the world championships in Kazan, Russia, in August.

"It is almost becoming the norm to go 53-low, 52-high now," she said.

"Everyone is going to have to step up their game now … me included."

Bronte Campbell, who qualified fastest for the final, was satisfied with her result.

"It was good," she said. "I made a few mistakes … missed the start a bit, missed my turn a bit but, to be honest, I am pretty happy with that.

"To be hitting around that 53.0 mark this early in the season is really exciting for me."

However, she was even happier for her elder sister, saying: "I'm unbelievably thrilled for Cate because she has had a really, really tough year.

"She has been racing with injury for over a year, and then for her to come back from surgery. So I'm so glad she could get up and do that."

Also on Wednesday Queensland's Mitch Larkin won the 200-metre backstroke final in 1:55.52 from Victorians Joshua Beaver (1:56.48) and Ashley Delaney (1:58.84).

Tessa Wallace won the 200-metre breaststroke final in 2:23.34 from fellow Queenslander Taylor McKeown (2:23.77) and South Australian Sally Hunter (2:24.38).

Queensland's Nicholas Schafer won the men's 200-metre breaststroke final in 2:13.21 from NSW's Matthew Wilson (2:13.33) and Queensland's Buster Sykes (2:14.04).

In the men's 4 x 200-metre freestyle relay final, Queensland's Miami club, with Daniel Smith, Thomas Fraser-Holmes, Jordan Harrison and Grant Hackett in the water, broke the Australian club record time of 7:10.24 on their way to victory. In second was Melbourne Vicentre (7:29.86) followed by Nunawading of Victoria (7:33.79).