The South African triumphed at the end of the 129.2 kilometre route from Unley to Campbelltown as the International Cycling Union (UCI) WorldTour race continued.

A breakaway group had threatened to stay clear for the duration of the stage, which concluded with an ascent of Corkscrew Road, followed by a fast-paced descent.

The group were eventually brought back by a reduced chasing pack, prior to the final climb.

Canada’s Michael Woods, New Zealand’s George Bennett, Australia’s Richie Porte and Wout Poels of the Netherlands then launched an attack on the climb.

The quartet were able to open up a gap on the climb but could not hold off a 16-rider chasing group on the descent.

A sprint finish then became an inevitability, with Impey proving the fastest of the finishers to have survived the climb.

The Mitchelton-Scott rider crossed the line in a winning time of 3hr, 3min and 27sec.

He was followed by race leader Patrick Bevin of New Zealand, with the CCC Team rider given the same time in second.

Spain’s Luis Leon Sanchez rounded off the top three.

Following the bonus seconds earned for the victory, Impey rose to second in the general classification.

The South African road race champion lies seven seconds adrift of Bevin, who remains in the race lead.

Sanchez is third at 11 seconds down.

Slovakia’s Peter Sagan, a three-time world road race champion, slipped down the standings after failing to make the lead group in the closing kilometres.

Having begun the day at one second off the lead, he is now 39 seconds off the pace in 20^th position.

The Australian race will continue tomorrow with the penultimate stage seeing riders tackle a 149.5km route from Glenelg to Strathalbyn.