Like many tall forwards, Day has struggled in his first two-and-bit seasons in the big time.
The 20-year-old South Australian was taken at No.3 in the 2010 AFL National Draft and suffered a knee injury that derailed his first season.
He kicked just 15 goals from his first 26 games.
But a long-term arm injury to experienced fullback Matthew Warnock forced the SUNS to shuffle the cards - that meant Day joining emerging defender Rory Thompson in the key defensive posts.
Since switching to defence in round five against Greater Western Sydney, the super athletic Day has looked far more comfortable and at home than he ever did forward.
Aside from a poor outing against Geelong last Saturday night, defensive coach Dean Solomon said Day was being viewed as more than a stop-gap measure in the back half.
"His month of football … is probably as good a football as he's played at the club," Solomon said.
"Right now we're probably looking to settle him down at centre half-back for the long term.
"If we can get good results out like we have the last month and keep increasing his output, there'd be no reason to move him forward or in the ruck."
Day played back at stages during the pre-season and appears to be capable of going with most players on the lead or in the air.
With Thompson deservedly taking most of the plaudits for his outstanding jobs on the opposition's best forward, Day has flown under the radar so far.
"I'm excited, no doubt about that," Solomon said.
"Both those key defenders have got a lot to learn and have to keep working on their game. They've showed some good signs gut they've got a lot to work on."
Day's emergence in defence might allow Nathan Bock – who played his first match in reserves last weekend after a year out – to play forward when he returns.
He may have been drafted as a forward, but there's no doubt SUNS coach Guy McKenna would be equally happy if Day locked down a key defensive post in the long term.
