At the start of last year, O'Shea had been pigeonholed as a key-position player.
The 192cm, 90kg teenager had spearheaded the Victoria Metro attack at the NAB AFL Under-16 Championships in 2008 and showed his wares in a key defensive post for the Eastern Ranges, but his decision to shed six kilograms set in motion the chain of events that saw him drafted by the Power on Thursday night.
O'Shea was not overweight, but changing his eating habits contributed to some major improvements on the field.
"I lost the weight by making some changes to my diet and also because of all the training I was doing," O'Shea said.
"My mum, Sharon, was really a great help. She started buying lean meat and low-fat milk and cheese, which helped me to keep my weight down."
The 18-year-old arrived for day one of the Ranges' pre-season training weighing just 86kg and quickly discovered his lighter frame made doing the basics, like running and jumping, much easier.
"Two pre-seasons ago when I weighed around 90kg I did a 14.1 beep test," O'Shea said.
"When I got down to 84kg I ran a 15.1, so I think dropping that weight has helped my game a fair bit. It's just given me a lot more freedom in the way I move."
O'Shea's improved fitness and mobility saw him released into the midfield and it was there he caught the eye of Port Adelaide, with coach Matthew Primus likening him to a young Chad Cornes.
An Emerald local, O'Shea was selected to represent Vic Metro at the under-18 championships, but he was denied the opportunity after injuring his finger in a work-place accident partway the tournament.
"It was pretty frustrating getting injured at work. I work for a company that produces banners. I wasn't concentrating on what I was doing for a second and I almost took the top of my finger off," O'Shea said.
"I had surgery to reattach it, which cost me five weeks on the sidelines. I still haven't got all the feeling back, but it doesn't really affect me."
O'Shea's interrupted carnival made him all the more determined to impress at the NAB AFL Draft Combine in October and impress he did.
The hard-running onballer finished second behind eventual No.4 draft pick Andrew Gaff in the 3km time trial in a time of 10mins 3secs, and seventh overall in the beep test.
He was snapped up with Port Adelaide's last live pick (No.52 overall) on Thursday night and will arrive in Adelaide on Sunday afternoon.
O'Shea, who is of Irish descent, is expected to make a quick transition to senior football, but said he wasn't going to set any goals for himself just yet.
"I just want to have a really big pre-season and see what happens from there. If I play next year I play, but I haven't really put any expectations on myself."
