Teenager James Magnussen beat Eamon Sullivan in the men's 100 meters freestyle final at the Australian Swimming Championships in Sydney on Tuesday night.

The 19-year-old won his first Australian title by finishing the men's 100 meters freestyle in 48.29, the quickest international time of 2011.

He has beat his previous best by 0.39 of a second, and finished ahead of fellow 19-year-old James Roberts (48.72) and highly-fancied Olympic silver medalist Sullivan (48.89).

Roberts and Magnussen has been qualified to join the Australian men' s 100 meters freestyle team to complete at the FINA World Championships in Shanghai of China, while Sullivan, Matt Targett (48.91) and Matthew Abood (48.95) also qualified for the 4x100m relay squad.

"For the past year I've been thinking about this race (Australian Championship) and thought I had a good chance of winning it," Magnussen told ABC Sports on Wednesday.

"It's been my aim since Commonwealth Games anyway to win this race and it's amazing to come out and do it."

"I've got complete faith in my back end speed and I knew if I was within striking distance of the boys I could get them. I possibly went out a bit harder than I have before but I was able to hang on for the finish."

Meanwhile, five-time Commonwealth Games gold medalist Alicia Coutts set the fastest time (54.27) in the semi-finals of the women' s 100 meters freestyle on Tuesday morning.

Yolane Kukla (54.49) went stroke-for-stroke with Coutts in the semifinal to qualify in second place, while Bronte Barratt (54.72), who has finished second in both the 200 meters and 400 meters freestyle this week, recorded the third quickest time.