The Orica-GreenEdge rider was the hot favourite rolling off the start ramp in Wartburg and stormed round the 48-kilometre course in just over an hour, beating second-placed Reinardt Janse van Rensburg by 44 seconds. Van Resburg's Dimension Data teammate Johann Van Zyl was third.
The victory is Impey's fifth title in six years and, after not competing in 2012, means he has been the victor on every occasion he has taken part.
"I'm pretty happy that each time I've started the elite champs I've been able to win," said Impey in a statement from the Orica-GreenEdge team. "There's always pressure coming here, because I've always been the favourite, so its a relief to come back here and back it up."
"I had a pretty tough fight out there from Reindardt, so I was just really happy to finish it off today and deliver when it mattered."
Impey started his season at the Tour Down Under last month, where, despite a crash on stage two, he played an important role in teammate Simon Gerrans' overall victory.
"I've worked really hard in December and January coming off Tour Down Under. After the crash I had, I needed a few extra days to take it easier and I freshened up nicely in to this," he added.
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"I am really pleased to be able to win on South African soil. It was great to have Miha (Peterlid) and Dean Edwards in the car following me, it kind of motivated me even more. They put a lot of effort in behind the scenes so it's nice to have support from the team and Dean."
The road race at the South African nationals takes place this Sunday and Impey, who has been runner-up for the past two editions, will be hoping to go one better and take the national jersey off the shoulders of Jacques Janse van Resnburg.
