With a target on his back as the sole Mitchelton-Scott rider, Dimension Data toyed with Impey early, getting Nicholas Dlamini in the day's break with Jayde Julius (ProTouch).
Dlamini attacked Julius with three laps to go and with no cooperation from Dimension Data riders behind in the bunch, Impey was forced to face the burden alone.
But the 34-year-old soon showed Dimension Data his heels, attacking the bunch on the final climb and overtaking Dlamini up the road to cross the finish 25 seconds ahead of Ryan Gibbons (Dimension Data).
"I just wanted to fight for it. Win, lose or draw. I wanted to go all in," Impey said.
“Even though they threw everything at me I rode intelligently and used my experience because I have been in this situation many times.
“I didn’t think I would be taking the jersey back to Europe just because I had the odds against me, just shows you it is never over till it's over. I am backing myself more and it is a great step forward in my career.
“I had massive support from my family and friends. History made again, I love doing the double!”
Just several days before, Impey also took out the South African national ITT title, his eighth in a row.