Porte attacked in the dying kilometres of the penultimate stage of the opening WorldTour race of the 2015 season, splitting the peloton on Willunga Hill.
Race leader Dennis put in a mammoth effort to minimise his time lose to Porte, managing to retain the ochre jersey going into Sunday’s final, flat stage.
Just two seconds separate Dennis and Porte overall, but with little opportunity for Porte to claw back any time, Dennis looks to have the race sewn up.
Welshman Geraint Thomas (Sky) had led the peloton going into the final climb, dropping Porte off for the stage win.
Cadel Evans (BMC), in his final WorldTour race before retirement, finished fourth on the stage to position himself in third overall.