After two senior games in three years with the Saints, Simpkin has played 14 of 17 matches this season, establishing himself as a key plank in the Saints' defence.
But as with most examples of a player improving out of sight, Simpkin's story has been one of perseverance rather than instant success.
Taken in the 2009 rookie draft, Simpkin battled shin problems in his first two seasons in the AFL system as he watched a dominant St Kilda team back up its Grand Final against Geelong with a repeat performance against Collingwood.
He was elevated to the senior list in 2011 and played two senior matches before seeing out the season in the VFL.
But it was at the end of last year that two major developments took place, paving the way for Simpkin to forge an AFL career.
The first was surgery to correct problems with his shins that had been hampering him for five years.
Simpkin had managed the problem while trying to prove himself with the Saints but realised he had to take drastic action to properly address it.
"It was crazy. There were days where I couldn't get out of bed in the morning," Simpkin told AFL.com.au.
"The docs said there was surgery that could be done so I wanted to get right into it straight away."
The second development was a flow-on from one of the most controversial coaching departures in the modern era.
Senior coach Ross Lyon had left for Fremantle, taking with him key defender Zac Dawson.
With fellow backman James Gwilt recovering from a knee reconstruction and a fresh set of coaching eyes in Scott Watters, Simpkin knew his chance had come to consolidate himself as a senior player.
"Once Zac left I knew there was an opportunity there. Obviously it wasn't going to be handed to me just because we were short on key backs, Scott let me know that straight away," he said
"On day one of pre-season I knew I had to work hard."
Simpkin has only missed three games this year, often taking on some of the AFL's premier tall forwards.
At 191cm and 91 kg, he concedes both size and profile to players such as Jack Riewoldt and Lance Franklin but says the experience of playing on the best in the business has improved his own game.
The idea of taking on Franklin under the MCG lights would be intimidating for most and Simpkin says he had to force himself to get past the Hawthorn star's aura and do his job when the two teams met in May.
"I wasn't on him for that long. Seany Dempster was on him for most of the game," he said.
"There was part of a quarter when I had to play on him and you think 'oh my god I'm next to Buddy Franklin, anything can happen here'. But you can't really think about it too much, you have to treat him like any other player."
Simpkin says he has been focusing on using his body strength rather than pace to beat his opponents, with some handy points from one of the best defenders in St Kilda's history, Max Hudghton.
Hudghton returned to the Saints in an assistant coaching role after two years with Collingwood and Simpkin says his tutelage has been invaluable.
"He's been great. Max was a star full back. To learn from him has been awesome all year," Simpkin said.
"He teaches me a lot about positioning - where to stand in reference to your opponent and the ball and also how to get the ball to the ground."
Luke Holmesby covers St Kilda news for AFL.com.au. Follow him on Twitter - @AFL_Luke
