SURPRISE St Kilda free agent Tim Membrey has marked a match-winning performance against Greater Western Sydney by inking a fresh contract extension.

Membrey was eligible under the 'free agency for life' clause this season, having previously been delisted by Sydney at the end of 2014.

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Now a Saints vice-captain and the leader of the club's attack, the 26-year-old forward has signed a new three-year deal tying him to RSEA Park until the end of 2024.

It comes off the back of a three-goal, 21-disposal outing against the Giants in which Membrey willed his side over the line in the final term with nine first-choice teammates, including Max King, Zak Jones, Paddy Ryder and Rowan Marshall, sidelined.

Teammates get around Tim Membrey against the Giants. Picture: AFL Photos

"I think we're really building towards something special and we've got the right people at the club," Membrey told AFL.com.au.

"We've recruited strongly with some gun players and I really do think the next few years are going to be exciting from here and I certainly want to be a part of that.

"(I'm) part of the leadership group now and I really feel like I've been there through the bad times and the good now and feel like with 'Ratts' (coach Brett Ratten) at the helm and some good assistants, and at the top with (CEO) Matty Finnis and (chief operating officer) Simon Lethlean, everyone's on the same page."

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Membrey's extension is a further fillip in a whirlwind career that had him contemplating his football future before the Saints came knocking ahead of 2015. 

After a single game for Sydney in 2014, Membrey has now booted 192 majors from 110 games at St Kilda.

"I still do pinch myself, I never really thought that I'd be a vice-captain of an AFL club after being delisted from Sydney," he said.

"It certainly didn't come easy early on in my career. I had to find out quickly how hard it really was to make it in the system and to be a consistent footballer.

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"I had great people to lean on up there in Sydney and now down here at St Kilda, I think I learnt my lessons early.

"(I learned) the real day-to-day grind and that there's a program that gets put in place as a footballer, but there's other things you can do to fast-track your football career.

"For me it was probably my fitness early days and now I feel like I'm at a level where I can compete and run out games strongly, and it's turned into one of my strengths.

"Finding out your weaknesses early and not being afraid to say that you have weaknesses and that you want to improve on them, I found like that was the biggest thing for me."

King, a player Membrey said he can't wait to see blossom over the next three years of his contract, will return alongside Jones against Melbourne on Saturday night in the inaugural 'Spud's Game' launched to tackle mental health.