Impey will enter the final sprint stage in a tie-break with Richie Porte (BMC), who conceded the ochre jersey to the South African after winning atop Willunga Hill for the fifth consecutive time on Saturday.
The 33-year-old Impey was considered an outsider at best from the beginning of the race in which he has worked diligently for sprinter Caleb Ewan.
Mitchelton-Scott sports director Matt White on Saturday claimed a top-five performance from Impey would have been sufficient, and described title victory as a "pipedream".
The pair were seen talking together and studying an overnight results sheet at the beginning of the queen stage, which Impey finished second behind Porte.
"I said at the start of the week and I'll say it again, he's the most versatile rider on our roster. He's certainly taken it to another level this year. He's got a big opportunity to fill the shoes of some of the guys who have left and he's taken it with two hands," White said.
"The primary goal has always been Caleb but we knew we could support Daryl. It's one of those tours if you get your combination of team right and ride smart you can do it."
Mitchelton-Scott has outlined dual goals at the Tour de France this year in which it will debut Ewan while supporting British climber Adam Yates in his overall bid.
There's conjecture as to whether such an approach at the Tour is profitable, but White has committed and took confidence from his squad's two-prong show in Adelaide.
"What I'm really, really proud of is the composure of the guys. It's hard coming in with multiple goals but we're going to do it at multiple races this year and it's a nice start," he said.
Impey echoed the sentiment.
"I put quite a bit of work back in South Africa [during the off-season] and it [Tour Down Under] really was a target but tried to keep it on the down-low," he said.
"It's fantastic to have the team support me the way they did, and to commit for Caleb and for me that was special."
Impey's result sheet from his many years at incarnations of Mitchelton-Scott is short, given he has typically been assigned to assist prolific winners - most notably Simon Gerrans.
White said he will receive more of his own opportunities this year.
"He's got some big, big targets coming up and I'm so proud of him. He's worked his arse off. This is the biggest win of his career and a massive win for the team," he said.