The family history has preceded the McKeon siblings, and on Thursday they fulfilled part of the legacy with Emma winning two gold medals and David a silver on the opening night of swimming events at the Commonwealth Games.

Emma won Australia's first swimming gold medal in the pool in the 200 metre freestyle final then took her part in the 4x100 freestyle relay team that broke the world record in the final race of the night. Olympic 200 metre freestyle bronze medallist Bronte Barratt won the bronze in 1:56.62 behind Siobhan O'Connor of England (1:55.82).

But David McKeon was not outshone by any means, swimming a remarkable race in the 400 freestyle, where he was under Paul Biedermann's supersuit-era world record pace through to the 300 metre mark, and was still leading the field at the final turn only for 1500 metre freestyle specialist Ryan Cochrane to overhaul him on the final lap.

The McKeon siblings come from a rich swimming bloodline. Ron McKeon swam at two Olympic Games and mother, Susie (formerly Woodhouse) competed at the 1982 Commonwealth Games, while uncle Rob Woodhouse was also an Olympic swimmer. Ron McKeon and Woodhouse also competed at Commonwealth Games and David McKeon has said when he won the national title last April that the family connection with the Games "meant a lot to me".

So after so much expectation, Emma McKeon said she was overwhelmed by the performances, with the relay world-record performance being her favoured moment.

"I wasn't expecting any of this," said Emma McKeon, who won in a  Games record, one minute 55.57. "I'm speechless."

"My family is just very proud of both me and my brother and they are just excited to see it."

Her brother, who turns 22 on Friday, had no doubt.

"I knew she could do that," David McKeon said. "She's pretty amazing my sister, what she does in training."

"It's awesome night for our family. They (parents) were just stoked. Full credit to coach (Vince) Raleigh and my dad who we've worked with and moving out of home which has helped us and dad's helped us by pushing us away a little bit.

"It has been hard, there's been a few ups and downs but I guess every one has that when they move out of home for the first time. It's all about having fun and having a good time."

David McKeon resisted the pull of family tradition into the competitive pool, revealing after making his first national team in 2012 that in his early teenage years he had only risen early in the morning to watch cheesy American television programs.

He only began to follow his swimming ambitions seriously when his father essentially forced him to do something useful. After a disappointing world championships last year, where he failed to make the final, David McKeon said he was "stoked" with winning the silver despite the late fade out, denying that he had gone out too hard.

"I've still got to work a little bit on my race plan and this is just a stepping stone through to Rio and I think I've put together a good day here," said McKeon, who also made the 2012 London Olympics team.

"I made the final so that was a big step for me.  When I started this sport four years ago I said this was the team I wanted to make and I wanted to go well here, this is my third year on the team so I can't ask more than that and to get a silver medal here, which is awesome."

McKeon said he had always intended to be on world record pace for as long as he could, confident that he could burn off the long distance swimmers in the field. However, he said he was surprised by the speed of Cochrane, who won in 3:43.46. David McKeon finished 3:44.09.

"I knew I had a good gap. I didn't think he had that much speed but I'm happy with that, real happy," McKeon said.

"They (long distance swimmers) haven't got the early speed to match what I'm doing so that was my upper hand and I think I raced it to the best of my ability.

"That's the way I race my race. That was a PB (personal best) for an international swimming (meet) so that's all I can ask for with the extra pressure and I learnt a lot from that tonight."

"I was a bit nervous in the marshalling area but I've been working on that. I'm stoked with how I went."

With that David McKeon was on his way. He had a more important commitment to keep.

"I've got to go and watch my sister," he said. He was glad that he did.