Originally on-loan from Heidelberg United in the second tier, the Athui took time to adapt to the rigours of professional football.
But the 25-year-old hit his straps late in the campaign with some outstanding shifts off the bench and coach Kevin Muscat said he "absolutely deserves this new contract".
"He's worked incredibly hard over the past six months to get himself into a position where he now has the physical capabilities to play at the top level," Muscat said.

"We saw him come into his own late in the season, not only getting himself a couple of goals, but more importantly he made an impact off the bench and influenced games."

That trait that was never more evident than in the dying stages of April's epic semi-final win over the Sky Blues.

Muscat added: "Not many would realise this, but it was actually Kenny's desperation that won the ball for Terry Antonis to score the winner against Sydney FC and get us into the Grand Final.
"Kenny's a big boy who moves well across the ground, so he's going to cause plenty of headaches and we're looking forward to seeing what he can do with a full pre-season under his belt."

Athiu is looking forward to building on his handful of senior appearances.

"I really enjoyed my first taste of professional football last season, it was a big step up but I had great support from everyone at the club," he said.

"I'm thankful to Kevin for the opportunity to extend my stay here and I'm determined to repay his faith in me."

Athiu is presently on leave and will return for pre-season training the week commencing July 9.