Once again the Australian beat world champion Peter Sagan, who finished second as he did on stage three, while Team Sky's Danny van Poppel took third.

Ewan, riding for ORICA-Scott, matched his 2016 haul of two stage wins yesterday but went on to surpass it in emphatic fashion today.

"I really couldn't have asked for a better start to the year," Ewan said.

"All the wins I've had in the past few days, the finishes have been really different.

"I knew this one was going to be tough."

The early stages of the leg were played out in familiar style, with a three-man break of Australia's Cameron Meyer, the 2011 tour winner, New Zealand's Jack Bauer and Ondrej Cink of the Czech Republic leading the way early on.

They were unable to put some space between themselves and the rest of the pack though and Cink struggled to maintain the pace as dropped back with around 55km remaining.

Meyer and Bauer then worked together to hold on to their lead for another 30km.

As Meyer began to tire, Bauer produced a sublime solo effort as he tired to hold off the rest of the pack. 

However, he was caught with just 4km remaining as Ewan found himself boxed in as the group approached the final stages.

Able to break free, Ewan then escaped the rest of the field and tore past van Poppel and Sagan to claim the win.

He has also retained the sprinters' jersey, six points ahead of van Poppel.

Tomorrow's 151.5km penultimate stage includes two climbs up Willunga Hill and will take riders through the McLaren Vale wine region.

Richie Porte has retained the leader's ochre jersey and remains 20 seconds ahead of his nearest rival, Spain's Gorka Izaguirre.

Izaguirre’s left arm and leg were swathed in bandages today as he prepared for the stage start.

The Movistar rider attained some nasty injuries after he was caught in a three-rider crash yesterday near the Victor Harbour finish.