The Mitchelton-Scott rider had begun the final stage with a 19-second buffer to eventual runner-up Richie Porte (Trek-Segafredo), and with the day's breakaway hoovering up the bonus seconds available on the stage's two intermediate sprints, it was going to come down to the final climb of Willunga Hill to decide the overall winner.
While Porte attacked to win on Willunga for the sixth year in a row, in an almost carbon copy of last year's race – when Impey and Porte finished with the same overall time, but Impey won the race overall in 'countback' – the South African was able to keep Porte within sight, and dug deep enough to latch on to second-placed Wout Poels (Team Sky) and finish third on the stage in the same time as a celebrating Porte.
The Australian took a 10-second bonus for the stage win, and Impey's third place gave him four seconds, which meant that Impey beat Porte overall by 13 seconds, with Poels third, another four seconds back.
Overnight race leader Patrick Bevin's injuries from his crash on stage 5 meant that the New Zealander was unable to follow the pace on the first ascent of Willunga Hill, and he fell well out of contention with more than 20 kilometres of the stage left to race.
"I felt sorry for Paddy," Impey told reporters after receiving the ochre leader's jersey on the podium. "I was looking forward to having a nice battle with him, and it's very sad that he wasn't in his best condition due to his crash.
"It feels as though he got a little bit robbed in the race, but that's bike racing, and there's not too much more you can say about it. But he's got guts. Coming to the start line today, you could see he was hurting, you could see he wasn't in good shape, so I felt sorry for him when I heard on the radio that he was in trouble," he said.
"He's definitely been the most consistent rider in this bike race, and would have been a really deserving winner as well."
Winning for the second year in a row was "special", Impey said, adding that he never really believed it would be possible.
"Every year we come here with a strong team with big ambitions, and this year when they said we were going to come here and back me with a full team to hopefully go 'back-to-back', I thought it would be nice, but I knew how tough the competition always is at the Tour Down Under.
"But I believed in myself, and the team believed in me, and it's been just fantastic to pull it off," Impey said. "Yesterday [stage 5], we really dug deep. The guys controlled the stage early on in the day and we took some valuable seconds there at the intermediate sprints.
"Coming into this Willunga stage, we wanted to have about 20 second on the climbing group that's here [Porte, Poels, MIchael Woods, George Bennett], and in the end it didn't really matter that much," he continued. "But I had a great climb today, and I think we just fought really hard."
Impey said that Friday's stage win in Campbelltown had given the team a lot of momentum, and made them believe that they truly had a chance of winning the race overall.
"We'd really ticked some boxes and given ourselves every chance to win this race," he said. "Last year I felt as though I'd made a really big step, but to back it up... I feel very happy to win, and feel as though I'm maturing more and more as a rider, so that's exciting."
Impey paid tribute to his whole Mitchelton-Scott team, and was thrilled that there'd be multiple reasons to celebrate in Adelaide on Sunday evening.
"If I didn't have Lucas [Hamilton] there for me in the final, I definitely wouldn't have been that close to Richie in the end – and especially on the day that I won the stage. He's a young rider but has big potential. But the whole team was fantastic – it wasn't only one guy. It's very important to state that Lucas and I can only do our job there in the final because of great team work.
"And with it being Mat Hayman's last race, it's extra special," Impey said. "We were going to celebrate tonight anyway, but to have lots of reasons to celebrate makes it a really special night."