Teenager David McKeon caused an upset and carried on a proud family tradition in taking out the men's 400m freestyle title at Olympic trials in Adelaide on Thursday night.

The Wollongong 19-year-old clocked 3 minutes 48.96 seconds to overpower race favourite Ryan Napoleon (3:47.93) in the final to book his ticket to the London Olympics.

McKeon will follow in the footsteps of his father Ron and uncle Rob Woodhouse, both former Olympic swimmers.

McKeon's 17-year-old sister Emma, who won gold at the 2010 Youth Olympic Games in Singapore, is also trying to win a spot on the team this week in the 100m freestyle.

"I'm overwhelmed. Dad's been there, my uncle's been there, so I'm following on this family tradition. It's great," McKeon said.

"It would be even more special to have my sister there .... it would be a perfect picture."

David McKeon gave up swimming when aged 12.

"I didn't really enjoy it," he said.

But seeing his younger sister travel to swim meets pricked his interest in resuming swimming.

His father Ron credited the sibling rivalry with producing another family Olympian.

"His sister was starting to emerge on the scene in some of the national youth teams," said Ron, who swam at the 1980 and 1984 Olympics.

"The sibling rivalry ... even school carnivals, Emma was quick and David couldn't even match her.

"I'll never forget the day at a regional school swimming carnival that he actually pipped her - and it was on.

"They're brother and sister and they're not without their rivalry in all sorts of things."

As McKeon touched in first place at Olympic selection trials, the family legacy continued.

"I kind of went as I felt through the race and just suddenly all came together at the end.

Napoleon also sealed a berth at his first Olympics, denying Rob Hurley (3:48.60) for the second individual berth.

Both McKeon and Napoleon will back up for the 200m freestyle on Friday and are both in the same heat as returning champion Ian Thorpe.

AAP